draft-bhutton-json-schema-01

draft-bhutton-json-schema-01
Internet-Draft
JSON Schema
June 2022
Wright, et al.
Expires 12 December 2022
[Page]
Workgroup:
Internet Engineering Task Force
Internet-Draft:
draft-bhutton-json-schema-01
Published:
10 June 2022
Intended Status:
Informational
Expires:
12 December 2022
Authors:
A. Wright,
Ed.
H. Andrews,
Ed.
B. Hutton,
Ed.
Postman
G. Dennis
JSON Schema: A Media Type for Describing JSON Documents
Abstract
JSON Schema defines the media type "application/schema+json", a JSON-based format
for describing the structure of JSON data.
JSON Schema asserts what a JSON document must look like,
ways to extract information from it,
and how to interact with it.
The "application/schema-instance+json" media type provides additional
feature-rich integration with "application/schema+json" beyond what can be offered
for "application/json" documents.
Note to Readers
The issues list for this draft can be found at
For additional information, see
To provide feedback, use this issue tracker, the communication methods listed on the
homepage, or email the document editors.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 12 December 2022.
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Provisions Relating to IETF Documents
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Table of Contents
1.
Introduction
JSON Schema is a JSON media type for defining the structure of JSON data. JSON Schema
is intended to define validation, documentation, hyperlink navigation, and interaction
control of JSON data.
This specification defines JSON Schema core terminology and mechanisms, including
pointing to another JSON Schema by reference,
dereferencing a JSON Schema reference,
specifying the dialect being used,
specifying a dialect's vocabulary requirements,
and defining the expected output.
Other specifications define the vocabularies that perform assertions about validation,
linking, annotation, navigation, and interaction.
2.
Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in
RFC 2119
RFC2119
The terms "JSON", "JSON text", "JSON value", "member", "element", "object", "array",
"number", "string", "boolean", "true", "false", and "null" in this document are to
be interpreted as defined in
RFC 8259
RFC8259
3.
Overview
This document proposes a new media type "application/schema+json" to identify a JSON
Schema for describing JSON data.
It also proposes a further optional media type, "application/schema-instance+json",
to provide additional integration features.
JSON Schemas are themselves JSON documents.
This, and related specifications, define keywords allowing authors to describe JSON
data in several ways.
JSON Schema uses keywords to assert constraints on JSON instances or annotate those
instances with additional information. Additional keywords are used to apply
assertions and annotations to more complex JSON data structures, or based on
some sort of condition.
To facilitate re-use, keywords can be organized into vocabularies. A vocabulary
consists of a list of keywords, together with their syntax and semantics.
A dialect is defined as a set of vocabularies and their required support
identified in a meta-schema.
JSON Schema can be extended either by defining additional vocabularies,
or less formally by defining additional keywords outside of any vocabulary.
Unrecognized individual keywords simply have their values collected as annotations,
while the behavior with respect to an unrecognized vocabulary can be controlled
when declaring which vocabularies are in use.
This document defines a core vocabulary that MUST be supported by any
implementation, and cannot be disabled. Its keywords are each prefixed
with a "$" character to emphasize their required nature. This vocabulary
is essential to the functioning of the "application/schema+json" media
type, and is used to bootstrap the loading of other vocabularies.
Additionally, this document defines a RECOMMENDED vocabulary of keywords
for applying subschemas conditionally, and for applying subschemas to
the contents of objects and arrays. Either this vocabulary or one very
much like it is required to write schemas for non-trivial JSON instances,
whether those schemas are intended for assertion validation, annotation,
or both. While not part of the required core vocabulary, for maximum
interoperability this additional vocabulary is included in this document
and its use is strongly encouraged.
Further vocabularies for purposes such as structural validation or
hypermedia annotation are defined in other documents. These other
documents each define a dialect collecting the standard sets of
vocabularies needed to write schemas for that document's purpose.
4.
Definitions
4.1.
JSON Document
A JSON document is an information resource (series of octets) described by the
application/json media type.
In JSON Schema, the terms "JSON document", "JSON text", and "JSON value" are
interchangeable because of the data model it defines.
JSON Schema is only defined over JSON documents. However, any document or memory
structure that can be parsed into or processed according to the JSON Schema data
model can be interpreted against a JSON Schema, including media types like
CBOR
RFC7049
4.2.
Instance
A JSON document to which a schema is applied is known as an "instance".
JSON Schema is defined over "application/json" or compatible documents,
including media types with the "+json" structured syntax suffix.
Among these, this specification defines the "application/schema-instance+json"
media type which defines handling for fragments in the URI.
4.2.1.
Instance Data Model
JSON Schema interprets documents according to a data model. A JSON value
interpreted according to this data model is called an "instance".
An instance has one of six primitive types, and a range of possible values
depending on the type:
null:
A JSON "null" value
boolean:
A "true" or "false" value, from the JSON "true" or "false" value
object:
An unordered set of properties mapping a string to an instance, from the JSON "object" value
array:
An ordered list of instances, from the JSON "array" value
number:
An arbitrary-precision, base-10 decimal number value, from the JSON "number" value
string:
A string of Unicode code points, from the JSON "string" value
Whitespace and formatting concerns, including different lexical
representations of numbers that are equal within the data model, are thus
outside the scope of JSON Schema. JSON Schema
vocabularies
Section 8.1
that wish
to work with such differences in lexical representations SHOULD define
keywords to precisely interpret formatted strings within the data model
rather than relying on having the original JSON representation Unicode
characters available.
Since an object cannot have two properties with the same key, behavior for a
JSON document that tries to define two properties with
the same key in a single object is undefined.
Note that JSON Schema vocabularies are free to define their own extended
type system. This should not be confused with the core data model types
defined here. As an example, "integer" is a reasonable type for a
vocabulary to define as a value for a keyword, but the data model
makes no distinction between integers and other numbers.
4.2.2.
Instance Equality
Two JSON instances are said to be equal if and only if they are of the same type
and have the same value according to the data model. Specifically, this means:
both are null; or
both are true; or
both are false; or
both are strings, and are the same codepoint-for-codepoint; or
both are numbers, and have the same mathematical value; or
both are arrays, and have an equal value item-for-item; or
both are objects, and each property in one has exactly one property with
a key equal to the other's, and that other property has an equal
value.
Implied in this definition is that arrays must be the same length,
objects must have the same number of members,
properties in objects are unordered,
there is no way to define multiple properties with the same key,
and mere formatting differences (indentation, placement of commas, trailing
zeros) are insignificant.
4.2.3.
Non-JSON Instances
It is possible to use JSON Schema with a superset of the JSON Schema data model,
where an instance may be outside any of the six JSON data types.
In this case, annotations still apply; but most validation keywords will not be useful,
as they will always pass or always fail.
A custom vocabulary may define support for a superset of the core data model.
The schema itself may only be expressible in this superset;
for example, to make use of the "const" keyword.
4.3.
JSON Schema Documents
A JSON Schema document, or simply a schema, is a JSON document used to describe
an instance.
A schema can itself be interpreted as an instance, but SHOULD always be given
the media type "application/schema+json" rather than
"application/schema-instance+json". The "application/schema+json" media
type is defined to offer a superset of the
fragment identifier syntax and semantics provided by
"application/schema-instance+json".
A JSON Schema MUST be an object or a boolean.
4.3.1.
JSON Schema Objects and Keywords
Object properties that are applied to the instance are called keywords,
or schema keywords. Broadly speaking, keywords fall into one
of five categories:
identifiers:
control schema identification through setting a URI
for the schema and/or changing how the base URI is determined
assertions:
produce a boolean result when applied to an instance
annotations:
attach information to an instance for application use
applicators:
apply one or more subschemas to a particular location
in the instance, and combine or modify their results
reserved locations:
do not directly affect results, but reserve a place
for a specific purpose to ensure interoperability
Keywords may fall into multiple categories, although applicators
SHOULD only produce assertion results based on their subschemas'
results. They should not define additional constraints independent
of their subschemas.
Keywords which are properties within the same schema object are referred to as adjacent keywords.
Extension keywords, meaning those defined outside of this document
and its companions, are free to define other behaviors as well.
A JSON Schema MAY contain properties which are not schema keywords.
Unknown keywords SHOULD be treated as annotations, where the value
of the keyword is the value of the annotation.
An empty schema is a JSON Schema with no properties, or only unknown
properties.
4.3.2.
Boolean JSON Schemas
The boolean schema values "true" and "false" are trivial schemas that
always produce themselves as assertion results, regardless of the
instance value. They never produce annotation results.
These boolean schemas exist to clarify schema author intent and
facilitate schema processing optimizations. They behave identically
to the following schema objects (where "not" is part of the
subschema application vocabulary defined in this document).
true:
Always passes validation, as if the empty schema {}
false:
Always fails validation, as if the schema { "not": {} }
While the empty schema object is unambiguous, there are many
possible equivalents to the "false" schema. Using the boolean
values ensures that the intent is clear to both human readers
and implementations.
4.3.3.
Schema Vocabularies
A schema vocabulary, or simply a vocabulary, is a set of keywords,
their syntax, and their semantics. A vocabulary is generally organized
around a particular purpose. Different uses of JSON Schema, such
as validation, hypermedia, or user interface generation, will
involve different sets of vocabularies.
Vocabularies are the primary unit of re-use in JSON Schema, as schema
authors can indicate what vocabularies are required or optional in
order to process the schema. Since vocabularies are identified by URIs
in the meta-schema, generic implementations can load extensions to support
previously unknown vocabularies. While keywords can be supported outside
of any vocabulary, there is no analogous mechanism to indicate individual
keyword usage.
A schema vocabulary can be defined by anything from an informal description
to a standards proposal, depending on the audience and interoperability
expectations. In particular, in order to facilitate vocabulary use within
non-public organizations, a vocabulary specification need not be published
outside of its scope of use.
4.3.4.
Meta-Schemas
A schema that itself describes a schema is called a meta-schema.
Meta-schemas are used to validate JSON Schemas and specify which vocabularies
they are using.
Typically, a meta-schema will specify a set of vocabularies, and validate
schemas that conform to the syntax of those vocabularies. However, meta-schemas
and vocabularies are separate in order to allow meta-schemas to validate
schema conformance more strictly or more loosely than the vocabularies'
specifications call for. Meta-schemas may also describe and validate
additional keywords that are not part of a formal vocabulary.
4.3.5.
Root Schema and Subschemas and Resources
A JSON Schema resource is a schema which is
canonically
RFC6596
identified by an
absolute URI
RFC3986
. Schema resources MAY
also be identified by URIs, including URIs with fragments,
if the resulting secondary resource (as defined by
section 3.5 of RFC 3986
RFC3986
) is identical
to the primary resource. This can occur with the empty fragment,
or when one schema resource is embedded in another. Any such URIs
with fragments are considered to be non-canonical.
The root schema is the schema that comprises the entire JSON document
in question. The root schema is always a schema resource, where the
URI is determined as described in section
9.1.1
Note that documents that embed schemas in another format will not
have a root schema resource in this sense. Exactly how such usages
fit with the JSON Schema document and resource concepts will be
clarified in a future draft.
Some keywords take schemas themselves, allowing JSON Schemas to be nested:
"title": "root",
"items": {
"title": "array item"
In this example document, the schema titled "array item" is a subschema,
and the schema titled "root" is the root schema.
As with the root schema, a subschema is either an object or a boolean.
As discussed in section
8.2.1
, a JSON Schema document
can contain multiple JSON Schema resources. When used without qualification,
the term "root schema" refers to the document's root schema. In some
cases, resource root schemas are discussed. A resource's root schema
is its top-level schema object, which would also be a document root schema
if the resource were to be extracted to a standalone JSON Schema document.
Whether multiple schema resources are embedded or linked with a reference,
they are processed in the same way, with the same available behaviors.
5.
Fragment Identifiers
In accordance with section 3.1 of
RFC 6839
RFC6839
the syntax and semantics of fragment identifiers specified for
any +json media type SHOULD be as specified for "application/json".
(At publication of this document, there is no fragment identification
syntax defined for "application/json".)
Additionally, the "application/schema+json" media type supports two
fragment identifier structures: plain names and JSON Pointers.
The "application/schema-instance+json" media type supports one
fragment identifier structure: JSON Pointers.
The use of JSON Pointers as URI fragment identifiers is described in
RFC 6901
RFC6901
For "application/schema+json", which supports two fragment identifier syntaxes,
fragment identifiers matching the JSON Pointer syntax, including the empty string,
MUST be interpreted as JSON Pointer fragment identifiers.
Per the W3C's
best practices for fragment identifiers
W3C.WD-fragid-best-practices-20121025
plain name fragment identifiers in "application/schema+json" are reserved for referencing
locally named schemas. All fragment identifiers that do
not match the JSON Pointer syntax MUST be interpreted as
plain name fragment identifiers.
Defining and referencing a plain name fragment identifier within an
"application/schema+json" document are specified
in the
"$anchor" keyword
Section 8.2.2
section.
6.
General Considerations
6.1.
Range of JSON Values
An instance may be any valid JSON value as defined by
JSON
RFC8259
JSON Schema imposes no restrictions on type: JSON Schema can describe any JSON
value, including, for example, null.
6.2.
Programming Language Independence
JSON Schema is programming language agnostic, and supports the full range of
values described in the data model.
Be aware, however, that some languages and JSON parsers may not be able to
represent in memory the full range of values describable by JSON.
6.3.
Mathematical Integers
Some programming languages and parsers use different internal representations
for floating point numbers than they do for integers.
For consistency, integer JSON numbers SHOULD NOT be encoded with a fractional
part.
6.4.
Regular Expressions
Keywords MAY use regular expressions to express constraints, or constrain
the instance value to be a regular expression.
These regular expressions SHOULD be valid according to the regular expression
dialect described in
ECMA-262, section 21.2.1
ecma262
Regular expressions SHOULD be built with the "u" flag (or equivalent) to provide
Unicode support, or processed in such a way which provides Unicode support as
defined by ECMA-262.
Furthermore, given the high disparity in regular expression constructs support,
schema authors SHOULD limit themselves to the following regular expression
tokens:
individual Unicode characters, as defined by the
JSON specification
RFC8259
simple character classes ([abc]), range character classes ([a-z]);
complemented character classes ([^abc], [^a-z]);
simple quantifiers: "+" (one or more), "*" (zero or more), "?" (zero or
one), and their lazy versions ("+?", "*?", "??");
range quantifiers: "{x}" (exactly x occurrences), "{x,y}" (at least x, at
most y, occurrences), {x,} (x occurrences or more), and their lazy
versions;
the beginning-of-input ("^") and end-of-input ("$") anchors;
simple grouping ("(...)") and alternation ("|").
Finally, implementations MUST NOT take regular expressions to be
anchored, neither at the beginning nor at the end. This means, for instance,
the pattern "es" matches "expression".
6.5.
Extending JSON Schema
Additional schema keywords and schema vocabularies MAY be defined
by any entity. Save for explicit agreement, schema authors SHALL NOT
expect these additional keywords and vocabularies to be supported by
implementations that do not explicitly document such support.
Implementations SHOULD treat keywords they do not support as annotations,
where the value of the keyword is the value of the annotation.
Implementations MAY provide the ability to register or load handlers
for vocabularies that they do not support directly. The exact mechanism
for registering and implementing such handlers is implementation-dependent.
7.
Keyword Behaviors
JSON Schema keywords fall into several general behavior categories.
Assertions validate that an instance satisfies constraints, producing
a boolean result. Annotations attach information that applications
may use in any way they see fit.
Applicators apply subschemas to parts of the instance and combine
their results.
Extension keywords SHOULD stay within these categories, keeping in mind
that annotations in particular are extremely flexible. Complex behavior
is usually better delegated to applications on the basis of annotation
data than implemented directly as schema keywords. However, extension
keywords MAY define other behaviors for specialized purposes.
Evaluating an instance against a schema involves processing all of the
keywords in the schema against the appropriate locations within the instance.
Typically, applicator keywords are processed until a schema object with no
applicators (and therefore no subschemas) is reached. The appropriate
location in the instance is evaluated against the assertion and
annotation keywords in the schema object, and their results are gathered
into the parent schema according to the rules of the applicator.
Evaluation of a parent schema object can complete once all of its
subschemas have been evaluated, although in some circumstances evaluation
may be short-circuited due to assertion results. When annotations are
being collected, some assertion result short-circuiting is not possible
due to the need to examine all subschemas for annotation collection, including
those that cannot further change the assertion result.
7.1.
Lexical Scope and Dynamic Scope
While most JSON Schema keywords can be evaluated on their own,
or at most need to take into account the values or results of
adjacent keywords in the same schema object, a few have more
complex behavior.
The lexical scope of a keyword is determined by the nested JSON
data structure of objects and arrays. The largest such scope
is an entire schema document. The smallest scope is a single
schema object with no subschemas.
Keywords MAY be defined with a partial value, such as a URI-reference,
which must be resolved against another value, such as another
URI-reference or a full URI, which is found through the lexical
structure of the JSON document. The "$id", "$ref", and
"$dynamicRef" core keywords, and the "base" JSON Hyper-Schema
keyword, are examples of this sort of behavior.
Note that some keywords, such as "$schema", apply to the lexical
scope of the entire schema resource, and therefore MUST only
appear in a schema resource's root schema.
Other keywords may take into account the dynamic scope that
exists during the evaluation of a schema, typically together
with an instance document.
The outermost dynamic scope is the schema object at
which processing begins, even if it is not a schema resource root.
The path from this root schema to any particular keyword (that
includes any "$ref" and "$dynamicRef" keywords that may have
been resolved) is considered the keyword's "validation path."
Lexical and dynamic scopes align until a reference keyword
is encountered. While following the reference keyword moves processing
from one lexical scope into a different one, from the perspective
of dynamic scope, following a reference is no different from descending
into a subschema present as a value. A keyword on the far side of
that reference that resolves information through the dynamic scope
will consider the originating side of the reference to be their
dynamic parent, rather than examining the local lexically enclosing parent.
The concept of dynamic scope is primarily used with "$dynamicRef" and
"$dynamicAnchor", and should be considered an advanced feature
and used with caution when defining additional keywords. It also appears
when reporting errors and collected annotations, as it may be possible
to revisit the same lexical scope repeatedly with different dynamic
scopes. In such cases, it is important to inform the user of the
dynamic path that produced the error or annotation.
7.2.
Keyword Interactions
Keyword behavior MAY be defined in terms of the annotation results
of
subschemas
Section 4.3.5
and/or adjacent keywords
(keywords within the same schema object) and their subschemas.
Such keywords MUST NOT result in a circular dependency.
Keywords MAY modify their behavior based on the presence or absence
of another keyword in the same
schema object
Section 4.3
7.3.
Default Behaviors
A missing keyword MUST NOT produce a false assertion result, MUST
NOT produce annotation results, and MUST NOT cause any other schema
to be evaluated as part of its own behavioral definition.
However, given that missing keywords do not contribute annotations,
the lack of annotation results may indirectly change the behavior
of other keywords.
In some cases, the missing keyword assertion behavior of a keyword is
identical to that produced by a certain value, and keyword definitions
SHOULD note such values where known. However, even if the value which
produces the default behavior would produce annotation results if
present, the default behavior still MUST NOT result in annotations.
Because annotation collection can add significant cost in terms of both
computation and memory, implementations MAY opt out of this feature.
Keywords that are specified in terms of collected annotations SHOULD
describe reasonable alternate approaches when appropriate.
This approach is demonstrated by the
items
" and
additionalProperties
" keywords in this
document.
Note that when no such alternate approach is possible for a keyword,
implementations that do not support annotation collections will not
be able to support those keywords or vocabularies that contain them.
7.4.
Identifiers
Identifiers define URIs for a schema, or affect how such URIs are
resolved in
references
Section 8.2.3
, or both.
The Core vocabulary defined in this document defines several
identifying keywords, most notably "$id".
Canonical schema URIs MUST NOT change while processing an instance, but
keywords that affect URI-reference resolution MAY have behavior that
is only fully determined at runtime.
While custom identifier keywords are possible, vocabulary designers should
take care not to disrupt the functioning of core keywords. For example,
the "$dynamicAnchor" keyword in this specification limits its URI resolution
effects to the matching "$dynamicRef" keyword, leaving the behavior
of "$ref" undisturbed.
7.5.
Applicators
Applicators allow for building more complex schemas than can be accomplished
with a single schema object. Evaluation of an instance against a
schema document
Section 4.3
begins by applying
the
root schema
Section 4.3.5
to the complete instance
document. From there, keywords known as applicators are used to determine
which additional schemas are applied. Such schemas may be applied in-place
to the current location, or to a child location.
The schemas to be applied may be present as subschemas comprising all or
part of the keyword's value. Alternatively, an applicator may refer to
a schema elsewhere in the same schema document, or in a different one.
The mechanism for identifying such referenced schemas is defined by the
keyword.
Applicator keywords also define how subschema or referenced schema
boolean
assertion
Section 7.6
results are modified and/or combined to produce the boolean result
of the applicator. Applicators may apply any boolean logic operation
to the assertion results of subschemas, but MUST NOT introduce new
assertion conditions of their own.
Annotation
Section 7.7
results are
preserved along with the instance location and the location of
the schema keyword, so that applications can decide how to
interpret multiple values.
7.5.1.
Referenced and Referencing Schemas
As noted in
Section 7.5
, an applicator keyword may
refer to a schema to be applied, rather than including it as a
subschema in the applicator's value. In such situations, the
schema being applied is known as the referenced schema, while
the schema containing the applicator keyword is the referencing schema.
While root schemas and subschemas are static concepts based on a
schema's position within a schema document, referenced and referencing
schemas are dynamic. Different pairs of schemas may find themselves
in various referenced and referencing arrangements during the evaluation
of an instance against a schema.
For some by-reference applicators, such as
"$ref"
Section 8.2.3.1
, the referenced schema can be determined
by static analysis of the schema document's lexical scope. Others,
such as "$dynamicRef" (with "$dynamicAnchor"), may make use of dynamic
scoping, and therefore only be resolvable in the process of evaluating
the schema with an instance.
7.6.
Assertions
JSON Schema can be used to assert constraints on a JSON document, which
either passes or fails the assertions. This approach can be used to validate
conformance with the constraints, or document what is needed to satisfy them.
JSON Schema implementations produce a single boolean result when evaluating
an instance against schema assertions.
An instance can only fail an assertion that is present in the schema.
7.6.1.
Assertions and Instance Primitive Types
Most assertions only constrain values within a certain
primitive type. When the type of the instance is not of the type
targeted by the keyword, the instance is considered to conform
to the assertion.
For example, the "maxLength" keyword from the companion
validation vocabulary
json-schema-validation
will only restrict certain strings
(that are too long) from being valid. If the instance is a number,
boolean, null, array, or object, then it is valid against this assertion.
This behavior allows keywords to be used more easily with instances
that can be of multiple primitive types. The companion validation
vocabulary also includes a "type" keyword which can independently
restrict the instance to one or more primitive types. This allows
for a concise expression of use cases such as a function that might
return either a string of a certain length or a null value:
"type": ["string", "null"],
"maxLength": 255
If "maxLength" also restricted the instance type to be a string,
then this would be substantially more cumbersome to express because
the example as written would not actually allow null values.
Each keyword is evaluated separately unless explicitly specified
otherwise, so if "maxLength" restricted the instance to strings,
then including "null" in "type" would not have any useful effect.
7.7.
Annotations
JSON Schema can annotate an instance with information, whenever the instance
validates against the schema object containing the annotation, and all of its
parent schema objects. The information can be a simple value, or can be
calculated based on the instance contents.
Annotations are attached to specific locations in an instance.
Since many subschemas can be applied to any single
location, applications may need to decide how to handle differing
annotation values being attached to the same instance location by
the same schema keyword in different schema objects.
Unlike assertion results, annotation data can take a wide variety of forms,
which are provided to applications to use as they see fit. JSON Schema
implementations are not expected to make use of the collected information
on behalf of applications.
Unless otherwise specified, the value of an annotation keyword
is the keyword's value. However, other behaviors are possible.
For example,
JSON Hyper-Schema's
json-hyper-schema
"links" keyword is a complex annotation that produces a value based
in part on the instance data.
While "short-circuit" evaluation is possible for assertions, collecting
annotations requires examining all schemas that apply to an instance
location, even if they cannot change the overall assertion result.
The only exception is that subschemas of a schema object that has
failed validation MAY be skipped, as annotations are not retained
for failing schemas.
7.7.1.
Collecting Annotations
Annotations are collected by keywords that explicitly define
annotation-collecting behavior. Note that boolean schemas cannot
produce annotations as they do not make use of keywords.
A collected annotation MUST include the following information:
The name of the keyword that produces the annotation
The instance location to which it is attached, as a JSON Pointer
The schema location path, indicating how reference keywords
such as "$ref" were followed to reach the absolute schema location.
The absolute schema location of the attaching keyword, as a URI.
This MAY be omitted if it is the same as the schema location path
from above.
The attached value(s)
7.7.1.1.
Distinguishing Among Multiple Values
Applications MAY make decisions on which of multiple annotation values
to use based on the schema location that contributed the value.
This is intended to allow flexible usage. Collecting the schema location
facilitates such usage.
For example, consider this schema, which uses annotations and assertions from
the
Validation specification
json-schema-validation
Note that some lines are wrapped for clarity.
"title": "Feature list",
"type": "array",
"prefixItems": [
"title": "Feature A",
"properties": {
"enabled": {
"$ref": "#/$defs/enabledToggle",
"default": true
},
"title": "Feature B",
"properties": {
"enabled": {
"description": "If set to null, Feature B
inherits the enabled
value from Feature A",
"$ref": "#/$defs/enabledToggle"
],
"$defs": {
"enabledToggle": {
"title": "Enabled",
"description": "Whether the feature is enabled (true),
disabled (false), or under
automatic control (null)",
"type": ["boolean", "null"],
"default": null
In this example, both Feature A and Feature B make use of the re-usable
"enabledToggle" schema. That schema uses the "title", "description",
and "default" annotations. Therefore the application has to decide how
to handle the additional "default" value for Feature A, and the additional
"description" value for Feature B.
The application programmer and the schema author need to agree on the
usage. For this example, let's assume that they agree that the most
specific "default" value will be used, and any additional, more generic
"default" values will be silently ignored. Let's also assume that they
agree that all "description" text is to be used, starting with the most
generic, and ending with the most specific. This requires the schema
author to write descriptions that work when combined in this way.
The application can use the schema location path to determine which
values are which. The values in the feature's immediate "enabled"
property schema are more specific, while the values under the re-usable
schema that is referenced to with "$ref" are more generic. The schema
location path will show whether each value was found by crossing a
"$ref" or not.
Feature A will therefore use a default value of true, while Feature B
will use the generic default value of null. Feature A will only
have the generic description from the "enabledToggle" schema, while
Feature B will use that description, and also append its locally
defined description that explains how to interpret a null value.
Note that there are other reasonable approaches that a different application
might take. For example, an application may consider the presence of
two different values for "default" to be an error, regardless of their
schema locations.
7.7.1.2.
Annotations and Assertions
Schema objects that produce a false assertion result MUST NOT
produce any annotation results, whether from their own keywords
or from keywords in subschemas.
Note that the overall schema results may still include annotations
collected from other schema locations. Given this schema:
"oneOf": [
"title": "Integer Value",
"type": "integer"
},
"title": "String Value",
"type": "string"
Against the instance
"This is a string"
, the
title annotation "Integer Value" is discarded because the type assertion
in that schema object fails. The title annotation "String Value"
is kept, as the instance passes the string type assertions.
7.7.1.3.
Annotations and Applicators
In addition to possibly defining annotation results of their own,
applicator keywords aggregate the annotations collected in their
subschema(s) or referenced schema(s).
7.8.
Reserved Locations
A fourth category of keywords simply reserve a location to hold re-usable
components or data of interest to schema authors that is not suitable
for re-use. These keywords do not affect validation or annotation results.
Their purpose in the core vocabulary is to ensure that locations are
available for certain purposes and will not be redefined by extension
keywords.
While these keywords do not directly affect results, as explained in section
9.4.2
unrecognized
extension keywords that reserve locations for re-usable schemas may have
undesirable interactions with references in certain circumstances.
7.9.
Loading Instance Data
While none of the vocabularies defined as part of this or the associated documents
define a keyword which may target and/or load instance data, it is possible that
other vocabularies may wish to do so.
Keywords MAY be defined to use JSON Pointers or Relative JSON Pointers to examine
parts of an instance outside the current evaluation location.
Keywords that allow adjusting the location using a Relative JSON Pointer SHOULD
default to using the current location if a default is desireable.
8.
The JSON Schema Core Vocabulary
Keywords declared in this section, which all begin with "$", make up
the JSON Schema Core vocabulary. These keywords are either required in
order to process any schema or meta-schema, including those split across
multiple documents, or exist to reserve keywords for purposes that
require guaranteed interoperability.
The Core vocabulary MUST be considered mandatory at all times, in order
to bootstrap the processing of further vocabularies. Meta-schemas
that use the
"$vocabulary"
Section 8.1
keyword
to declare the vocabularies in use MUST explicitly list the Core vocabulary,
which MUST have a value of true indicating that it is required.
The behavior of a false value for this vocabulary (and only this
vocabulary) is undefined, as is the behavior when "$vocabulary"
is present but the Core vocabulary is not included. However, it
is RECOMMENDED that implementations detect these cases and raise
an error when they occur. It is not meaningful to declare that
a meta-schema optionally uses Core.
Meta-schemas that do not use "$vocabulary" MUST be considered to
require the Core vocabulary as if its URI were present with a value of true.
The current URI for the Core vocabulary is:
.
The current URI for the corresponding meta-schema is:
While the "$" prefix is not formally reserved for the Core vocabulary,
it is RECOMMENDED that extension keywords (in vocabularies or otherwise)
begin with a character other than "$" to avoid possible future collisions.
8.1.
Meta-Schemas and Vocabularies
Two concepts, meta-schemas and vocabularies, are used to inform an implementation
how to interpret a schema. Every schema has a meta-schema, which can be declared
using the "$schema" keyword.
The meta-schema serves two purposes:
Declaring the vocabularies in use
The "$vocabulary" keyword, when it appears in a meta-schema, declares
which vocabularies are available to be used in schemas that refer
to that meta-schema. Vocabularies define keyword semantics,
as well as their general syntax.
Describing valid schema syntax
A schema MUST successfully validate against its meta-schema, which
constrains the syntax of the available keywords. The syntax described
is expected to be compatible with the vocabularies declared; while
it is possible to describe an incompatible syntax, such a meta-schema
would be unlikely to be useful.
Meta-schemas are separate from vocabularies to allow for
vocabularies to be combined in different ways, and for meta-schema authors
to impose additional constraints such as forbidding certain keywords, or
performing unusually strict syntactical validation, as might be done
during a development and testing cycle. Each vocabulary typically identifies
a meta-schema consisting only of the vocabulary's keywords.
Meta-schema authoring is an advanced usage of JSON Schema, so the design of
meta-schema features emphasizes flexibility over simplicity.
8.1.1.
The "$schema" Keyword
The "$schema" keyword is both used as a JSON Schema dialect identifier and
as the identifier of a resource which is itself a JSON Schema, which describes the
set of valid schemas written for this particular dialect.
The value of this keyword MUST be a
URI
RFC3986
(containing a scheme) and this URI MUST be normalized.
The current schema MUST be valid against the meta-schema identified by this URI.
If this URI identifies a retrievable resource, that resource SHOULD be of
media type "application/schema+json".
The "$schema" keyword SHOULD be used in the document root schema object,
and MAY be used in the root schema objects of embedded schema resources.
It MUST NOT appear in non-resource root schema objects. If absent from
the document root schema, the resulting behavior is implementation-defined.
Values for this property are defined elsewhere in this and other documents,
and by other parties.
8.1.2.
The "$vocabulary" Keyword
The "$vocabulary" keyword is used in meta-schemas to identify the
vocabularies available for use in schemas described by that meta-schema.
It is also used to indicate whether each vocabulary is required or optional,
in the sense that an implementation MUST understand the required vocabularies
in order to successfully process the schema. Together, this information forms
a dialect. Any vocabulary that is understood by the implementation MUST be
processed in a manner consistent with the semantic definitions contained
within the vocabulary.
The value of this keyword MUST be an object. The property names in the
object MUST be URIs (containing a scheme) and this URI MUST be normalized.
Each URI that appears as a property name identifies a specific set of
keywords and their semantics.
The URI MAY be a URL, but the nature of the retrievable resource is
currently undefined, and reserved for future use. Vocabulary authors
MAY use the URL of the vocabulary specification, in a human-readable
media type such as text/html or text/plain, as the vocabulary URI.
Vocabulary documents may be added in forthcoming drafts.
For now, identifying the keyword set is deemed sufficient as that,
along with meta-schema validation, is how the current "vocabularies"
work today. Any future vocabulary document format will be specified
as a JSON document, so using text/html or other non-JSON formats
in the meantime will not produce any future ambiguity.
The values of the object properties MUST be booleans.
If the value is true, then implementations that do not recognize
the vocabulary MUST refuse to process any schemas that declare
this meta-schema with "$schema". If the value is false, implementations
that do not recognize the vocabulary SHOULD proceed with processing
such schemas. The value has no impact if the implementation
understands the vocabulary.
Per
6.5
, unrecognized
keywords SHOULD be treated as annotations.
This remains the case for keywords defined
by unrecognized vocabularies. It is not currently possible to distinguish
between unrecognized keywords that are defined in vocabularies from
those that are not part of any vocabulary.
The "$vocabulary" keyword SHOULD be used in the root schema of any schema
document intended for use as a meta-schema. It MUST NOT appear in subschemas.
The "$vocabulary" keyword MUST be ignored in schema documents that
are not being processed as a meta-schema. This allows validating
a meta-schema M against its own meta-schema M' without requiring
the validator to understand the vocabularies declared by M.
8.1.2.1.
Default vocabularies
If "$vocabulary" is absent, an implementation MAY determine
behavior based on the meta-schema if it is recognized from the
URI value of the referring schema's "$schema" keyword.
This is how behavior (such as Hyper-Schema usage) has been
recognized prior to the existence of vocabularies.
If the meta-schema, as referenced by the schema, is not recognized,
or is missing, then the behavior is implementation-defined.
If the implementation
proceeds with processing the schema, it MUST assume the use of the
core vocabulary. If the implementation is built for a specific purpose,
then it SHOULD assume the use of all of the most relevant vocabularies
for that purpose.
For example, an implementation that is a validator
SHOULD assume the use of all vocabularies in this
specification and the companion Validation specification.
8.1.2.2.
Non-inheritability of vocabularies
Note that the processing restrictions on "$vocabulary" mean that
meta-schemas that reference other meta-schemas using "$ref" or
similar keywords do not automatically inherit the vocabulary
declarations of those other meta-schemas. All such declarations
must be repeated in the root of each schema document intended
for use as a meta-schema. This is demonstrated in
the example meta-schema
Appendix D.2
This requirement allows implementations to find all vocabulary
requirement information in a single place for each meta-schema.
As schema extensibility means that there are endless potential
ways to combine more fine-grained meta-schemas by reference,
requiring implementations to anticipate all possibilities and
search for vocabularies in referenced meta-schemas would
be overly burdensome.
8.1.3.
Updates to Meta-Schema and Vocabulary URIs
Updated vocabulary and meta-schema URIs MAY be published between
specification drafts in order to correct errors. Implementations
SHOULD consider URIs dated after this specification draft and
before the next to indicate the same syntax and semantics
as those listed here.
8.2.
Base URI, Anchors, and Dereferencing
To differentiate between schemas in a vast ecosystem, schemas are
identified by
URI
RFC3986
, and can embed references
to other schemas by specifying their URI.
Several keywords can accept a relative
URI-reference
RFC3986
or a value used to construct a relative URI-reference. For these keywords,
it is necessary to establish a base URI in order to resolve the reference.
8.2.1.
The "$id" Keyword
The "$id" keyword identifies a schema resource with its
canonical
RFC6596
URI.
Note that this URI is an identifier and not necessarily a network locator.
In the case of a network-addressable URL, a schema need not be downloadable
from its canonical URI.
If present, the value for this keyword MUST be a string, and MUST represent a
valid
URI-reference
RFC3986
. This URI-reference
SHOULD be normalized, and MUST resolve to an
absolute-URI
RFC3986
(without a fragment),
or to a URI with an empty fragment.
The empty fragment form is NOT RECOMMENDED and is retained only
for backwards compatibility, and because the
application/schema+json media type defines that a URI with an
empty fragment identifies the same resource as the same URI
with the fragment removed. However, since this equivalence is not
part of the
RFC 3986 normalization process
RFC3986
implementers and schema authors cannot rely on generic URI libraries
understanding it.
Therefore, "$id" MUST NOT contain a non-empty fragment, and SHOULD NOT
contain an empty fragment. The absolute-URI form MUST be considered
the canonical URI, regardless of the presence or absence of an empty fragment.
An empty fragment is currently allowed because older meta-schemas have
an empty fragment in their $id (or previously, id).
A future draft may outright forbid even empty fragments in "$id".
The absolute-URI also serves as the base URI for relative URI-references
in keywords within the schema resource, in accordance with
RFC 3986 section 5.1.1
RFC3986
regarding base URIs
embedded in content.
The presence of "$id" in a subschema indicates that the subschema constitutes
a distinct schema resource within a single schema document. Furthermore,
in accordance with
RFC 3986 section 5.1.2
RFC3986
regarding encapsulating entities, if an "$id" in a subschema is a relative
URI-reference, the base URI for resolving that reference is the URI of
the parent schema resource.
If no parent schema object explicitly identifies itself as a resource
with "$id", the base URI is that of the entire document, as established
by the steps given in the
previous section.
Section 9.1.1
8.2.1.1.
Identifying the root schema
The root schema of a JSON Schema document SHOULD contain an "$id" keyword
with an
absolute-URI
RFC3986
(containing a scheme,
but no fragment).
8.2.2.
Defining location-independent identifiers
Using JSON Pointer fragments requires knowledge of the structure of the schema.
When writing schema documents with the intention to provide re-usable
schemas, it may be preferable to use a plain name fragment that is not tied to
any particular structural location. This allows a subschema to be relocated
without requiring JSON Pointer references to be updated.
The "$anchor" and "$dynamicAnchor" keywords are used to specify such
fragments. They are identifier keywords that can only be used to create
plain name fragments, rather than absolute URIs as seen with "$id".
The base URI to which the resulting fragment is appended is the canonical
URI of the schema resource containing the "$anchor" or "$dynamicAnchor"
in question. As discussed in the previous section, this is either the
nearest "$id" in the same or parent schema object, or the base URI
for the document as determined according to RFC 3986.
Separately from the usual usage of URIs, "$dynamicAnchor"
indicates that the fragment is an extension point when used with
the "$dynamicRef" keyword. This low-level, advanced feature
makes it easier to extend recursive schemas such as the meta-schemas,
without imposing any particular semantics on that extension.
See the section on
"$dynamicRef"
Section 8.2.3.2
for details.
In most cases, the normal fragment behavior both suffices and
is more intuitive. Therefore it is RECOMMENDED that "$anchor"
be used to create plain name fragments unless there is a clear
need for "$dynamicAnchor".
If present, the value of this keyword MUST be a string and MUST start with
a letter ([A-Za-z]) or underscore ("_"), followed by any number of letters,
digits ([0-9]), hyphens ("-"), underscores ("_"), and periods (".").
This matches the US-ASCII part of XML's
NCName production
xml-names
Note that the anchor string does not include the "#" character,
as it is not a URI-reference. An "$anchor": "foo" becomes the
fragment "#foo" when used in a URI. See below for full examples.
The effect of specifying the same fragment name multiple times within
the same resource, using any combination of "$anchor" and/or
"$dynamicAnchor", is undefined. Implementations MAY
raise an error if such usage is detected.
8.2.3.
Schema References
Several keywords can be used to reference a schema which is to be applied to the
current instance location. "$ref" and "$dynamicRef" are applicator
keywords, applying the referenced schema to the instance.
As the values of "$ref" and "$dynamicRef" are URI References, this allows
the possibility to externalise or divide a schema across multiple files,
and provides the ability to validate recursive structures through
self-reference.
The resolved URI produced by these keywords is not necessarily a network
locator, only an identifier. A schema need not be downloadable from the
address if it is a network-addressable URL, and implementations SHOULD NOT
assume they should perform a network operation when they encounter
a network-addressable URI.
8.2.3.1.
Direct References with "$ref"
The "$ref" keyword is an applicator that is used to reference a statically
identified schema. Its results are the results of the referenced schema.
Note that this definition of how the results are determined means that
other keywords can appear alongside of "$ref" in the same schema object.
The value of the "$ref" keyword MUST be a string which is a URI-Reference.
Resolved against the current URI base, it produces the URI of the schema
to apply. This resolution is safe to perform on schema load, as the
process of evaluating an instance cannot change how the reference resolves.
8.2.3.2.
Dynamic References with "$dynamicRef"
The "$dynamicRef" keyword is an applicator that allows for deferring the
full resolution until runtime, at which point it is resolved each time it is
encountered while evaluating an instance.
Together with "$dynamicAnchor", "$dynamicRef" implements a cooperative
extension mechanism that is primarily useful with recursive schemas
(schemas that reference themselves). Both the extension point and the
runtime-determined extension target are defined with "$dynamicAnchor",
and only exhibit runtime dynamic behavior when referenced with
"$dynamicRef".
The value of the "$dynamicRef" property MUST be a string which is
a URI-Reference. Resolved against the current URI base, it produces
the URI used as the starting point for runtime resolution. This initial
resolution is safe to perform on schema load.
If the initially resolved starting point URI includes a fragment that
was created by the "$dynamicAnchor" keyword, the initial URI MUST be
replaced by the URI (including the fragment) for the outermost schema
resource in the
dynamic scope
Section 7.1
that defines
an identically named fragment with "$dynamicAnchor".
Otherwise, its behavior is identical to "$ref", and no runtime
resolution is needed.
For a full example using these keyword, see appendix
The difference between the hyper-schema meta-schema in pre-2019
drafts and an this draft dramatically demonstrates the utility
of these keywords.
8.2.4.
Schema Re-Use With "$defs"
The "$defs" keyword reserves a location for schema
authors to inline re-usable JSON Schemas into a more general schema.
The keyword does not directly affect the validation result.
This keyword's value MUST be an object.
Each member value of this object MUST be a valid JSON Schema.
As an example, here is a schema describing an array of positive
integers, where the positive integer constraint is a subschema in
"$defs":
"type": "array",
"items": { "$ref": "#/$defs/positiveInteger" },
"$defs": {
"positiveInteger": {
"type": "integer",
"exclusiveMinimum": 0
8.3.
Comments With "$comment"
This keyword reserves a location for comments from schema authors
to readers or maintainers of the schema.
The value of this keyword MUST be a string. Implementations MUST NOT present this
string to end users. Tools for editing schemas SHOULD support displaying and
editing this keyword. The value of this keyword MAY be used in debug or error
output which is intended for developers making use of schemas.
Schema vocabularies SHOULD allow "$comment" within any object containing
vocabulary keywords. Implementations MAY assume "$comment" is allowed
unless the vocabulary specifically forbids it. Vocabularies MUST NOT
specify any effect of "$comment" beyond what is described in this
specification.
Tools that translate other media types or programming languages
to and from application/schema+json MAY choose to convert that media type or
programming language's native comments to or from "$comment" values.
The behavior of such translation when both native comments and "$comment"
properties are present is implementation-dependent.
Implementations MAY strip "$comment" values at any point during processing.
In particular, this allows for shortening schemas when the size of deployed
schemas is a concern.
Implementations MUST NOT take any other action based on the presence, absence,
or contents of "$comment" properties. In particular, the value of "$comment"
MUST NOT be collected as an annotation result.
9.
Loading and Processing Schemas
9.1.
Loading a Schema
9.1.1.
Initial Base URI
RFC3986 Section 5.1
RFC3986
defines how to determine the
default base URI of a document.
Informatively, the initial base URI of a schema is the URI at which it was
found, whether that was a network location, a local filesystem, or any other
situation identifiable by a URI of any known scheme.
If a schema document defines no explicit base URI with "$id"
(embedded in content), the base URI is that determined per
RFC 3986 section 5
RFC3986
If no source is known, or no URI scheme is known for the source, a suitable
implementation-specific default URI MAY be used as described in
RFC 3986 Section 5.1.4
RFC3986
. It is RECOMMENDED
that implementations document any default base URI that they assume.
If a schema object is embedded in a document of another media type, then
the initial base URI is determined according to the rules of that
media type.
Unless the "$id" keyword described in an earlier section is present in the
root schema, this base URI SHOULD be considered the canonical URI of the
schema document's root schema resource.
9.1.2.
Loading a referenced schema
The use of URIs to identify remote schemas does not necessarily mean anything is downloaded,
but instead JSON Schema implementations SHOULD understand ahead of time which schemas they will be using,
and the URIs that identify them.
When schemas are downloaded,
for example by a generic user-agent that does not know until runtime which schemas to download,
see
Usage for Hypermedia
Section 9.5.1
Implementations SHOULD be able to associate arbitrary URIs with an arbitrary
schema and/or automatically associate a schema's "$id"-given URI, depending
on the trust that the validator has in the schema. Such URIs and schemas
can be supplied to an implementation prior to processing instances, or may
be noted within a schema document as it is processed, producing associations
as shown in appendix
A schema MAY (and likely will) have multiple URIs, but there is no way for a
URI to identify more than one schema. When multiple schemas try to identify
as the same URI, validators SHOULD raise an error condition.
9.1.3.
Detecting a Meta-Schema
Implementations MUST recognize a schema as a meta-schema if it
is being examined because it was identified as such by another
schema's "$schema" keyword. This means that a single schema
document might sometimes be considered a regular schema, and
other times be considered a meta-schema.
In the case of examining a schema which is its own meta-schema,
when an implementation begins processing it as a regular schema,
it is processed under those rules. However, when loaded a second
time as a result of checking its own "$schema" value, it is treated
as a meta-schema. So the same document is processed both ways in
the course of one session.
Implementations MAY allow a schema to be explicitly passed as a meta-schema,
for implementation-specific purposes, such as pre-loading a commonly
used meta-schema and checking its vocabulary support requirements
up front. Meta-schema authors MUST NOT expect such features to be
interoperable across implementations.
9.2.
Dereferencing
Schemas can be identified by any URI that has been given to them, including
a JSON Pointer or their URI given directly by "$id". In all cases,
dereferencing a "$ref" reference involves first resolving its value as a
URI reference against the current base URI per
RFC 3986
RFC3986
If the resulting URI identifies a schema within the current document, or
within another schema document that has been made available to the implementation,
then that schema SHOULD be used automatically.
For example, consider this schema:
"$id": "https://example.net/root.json",
"items": {
"type": "array",
"items": { "$ref": "#item" }
},
"$defs": {
"single": {
"$anchor": "item",
"type": "object",
"additionalProperties": { "$ref": "other.json" }
When an implementation encounters the <#/$defs/single> schema,
it resolves the "$anchor" value as a fragment name against the current
base URI to form .
When an implementation then looks inside the <#/items> schema, it
encounters the <#item> reference, and resolves this to
, which it has seen defined in
this same document and can therefore use automatically.
When an implementation encounters the reference to "other.json", it resolves
this to , which is not defined in this
document. If a schema with that identifier has otherwise been supplied to
the implementation, it can also be used automatically.
What should implementations do when the referenced schema is not known?
Are there circumstances in which automatic network dereferencing is
allowed? A same origin policy? A user-configurable option? In the
case of an evolving API described by Hyper-Schema, it is expected that
new schemas will be added to the system dynamically, so placing an
absolute requirement of pre-loading schema documents is not feasible.
9.2.1.
JSON Pointer fragments and embedded schema resources
Since JSON Pointer URI fragments are constructed based on the structure
of the schema document, an embedded schema resource and its subschemas
can be identified by JSON Pointer fragments relative to either its own
canonical URI, or relative to any containing resource's URI.
Conceptually, a set of linked schema resources should behave
identically whether each resource is a separate document connected with
schema references
Section 8.2.3
, or is structured as
a single document with one or more schema resources embedded as
subschemas.
Since URIs involving JSON Pointer fragments relative to the parent
schema resource's URI cease to be valid when the embedded schema
is moved to a separate document and referenced, applications and schemas
SHOULD NOT use such URIs to identify embedded schema resources or
locations within them.
Consider the following schema document that contains another
schema resource embedded within it:
"$id": "https://example.com/foo",
"items": {
"$id": "https://example.com/bar",
"additionalProperties": { }
The URI "https://example.com/foo#/items" points to the "items" schema,
which is an embedded resource. The canonical URI of that schema
resource, however, is "https://example.com/bar".
For the "additionalProperties" schema within that embedded resource,
the URI "https://example.com/foo#/items/additionalProperties" points
to the correct object, but that object's URI relative to its resource's
canonical URI is "https://example.com/bar#/additionalProperties".
Now consider the following two schema resources linked by reference
using a URI value for "$ref":
"$id": "https://example.com/foo",
"items": {
"$ref": "bar"

"$id": "https://example.com/bar",
"additionalProperties": { }
Here we see that "https://example.com/bar#/additionalProperties",
using a JSON Pointer fragment appended to the canonical URI of
the "bar" schema resource, is still valid, while
"https://example.com/foo#/items/additionalProperties", which relied
on a JSON Pointer fragment appended to the canonical URI of the
"foo" schema resource, no longer resolves to anything.
Note also that "https://example.com/foo#/items" is valid in both
arrangements, but resolves to a different value. This URI ends up
functioning similarly to a retrieval URI for a resource. While this URI
is valid, it is more robust to use the "$id" of the embedded or referenced
resource unless it is specifically desired to identify the object containing
the "$ref" in the second (non-embedded) arrangement.
An implementation MAY choose not to support addressing schema resource
contents by URIs using a base other than the resource's canonical URI,
plus a JSON Pointer fragment relative to that base. Therefore, schema
authors SHOULD NOT rely on such URIs, as using them may reduce interoperability.
This is to avoid requiring implementations to keep track of a whole
stack of possible base URIs and JSON Pointer fragments for each,
given that all but one will be fragile if the schema resources
are reorganized. Some
have argued that this is easy so there is
no point in forbidding it, while others have argued that it complicates
schema identification and should be forbidden. Feedback on this
topic is encouraged.
After some discussion, we feel that we need to remove the use of
"canonical" in favour of talking about JSON Pointers which reference
across schema resource boundaries as undefined or even forbidden behavior
(https://github.com/json-schema-org/json-schema-spec/issues/937,
Further examples of such non-canonical URI construction, as well as
the appropriate canonical URI-based fragments to use instead,
are provided in appendix
9.3.
Compound Documents
A Compound Schema Document is defined as a JSON document (sometimes called a "bundled" schema)
which has multiple embedded JSON Schema Resources bundled into the same document to
ease transportation.
Each embedded Schema Resource MUST be treated as an individual Schema Resource, following standard
schema loading and processing requirements, including determining vocabulary support.
9.3.1.
Bundling
The bundling process for creating a Compound Schema Document is defined as taking
references (such as "$ref") to an external Schema Resource and embedding the referenced
Schema Resources within the referring document. Bundling SHOULD be done in such a way that
all URIs (used for referencing) in the base document and any referenced/embedded
documents do not require altering.
Each embedded JSON Schema Resource MUST identify itself with a URI using the "$id" keyword,
and SHOULD make use of the "$schema" keyword to identify the dialect it is using, in the root of the
schema resource. It is RECOMMENDED that the URI identifier value of "$id" be an Absolute URI.
When the Schema Resource referenced by a by-reference applicator is bundled, it is RECOMMENDED that
the Schema Resource be located as a value of a "$defs" object at the containing schema's root.
The key of the "$defs" for the now embedded Schema Resource MAY be the "$id" of the bundled schema
or some other form of application defined unique identifer (such as a UUID). This key is not
intended to be referenced in JSON Schema, but may be used by an application to aid the
bundling process.
A Schema Resource MAY be embedded in a location other than "$defs" where the location is defined
as a schema value.
A Bundled Schema Resource MUST NOT be bundled by replacing the schema object from which it was
referenced, or by wrapping the Schema Resource in other applicator keywords.
In order to produce identical output, references in the containing schema document to the
previously external Schema Resources MUST NOT be changed, and now resolve to a schema using the
"$id" of an embedded Schema Resource. Such identical output includes validation evaluation and URIs
or paths used in resulting annotations or errors.
While the bundling process will often be the main method for creating a Compound Schema Document,
it is also possible and expected that some will be created by hand, potentially without individual
Schema Resources existing on their own previously.
9.3.2.
Differing and Default Dialects
When multiple schema resources are present in a single document,
schema resources which do not define with which dialect they should be processed
MUST be processed with the same dialect as the enclosing resource.
Since any schema that can be referenced can also be embedded, embedded schema resources MAY
specify different processing dialects using the "$schema" values from their enclosing resource.
9.3.3.
Validating
Given that a Compound Schema Document may have embedded resources which identify as using different
dialects, these documents SHOULD NOT be validated by applying a meta-schema
to the Compound Schema Document as an instance. It is RECOMMENDED that an alternate
validation process be provided in order to validate Schema Documents. Each Schema Resource
SHOULD be separately validated against its associated meta-schema.
If you know a schema is what's being validated, you can identify if the schemas
is a Compound Schema Document or not, by way of use of "$id", which identifies an
embedded resource when used not at the document's root.
A Compound Schema Document in which all embedded resources identify as using the same
dialect, or in which "$schema" is omitted and therefore defaults to that of the enclosing resource,
MAY be validated by applying the appropriate meta-schema.
9.4.
Caveats
9.4.1.
Guarding Against Infinite Recursion
A schema MUST NOT be run into an infinite loop against an instance. For
example, if two schemas "#alice" and "#bob" both have an "allOf" property
that refers to the other, a naive validator might get stuck in an infinite
recursive loop trying to validate the instance. Schemas SHOULD NOT make
use of infinite recursive nesting like this; the behavior is undefined.
9.4.2.
References to Possible Non-Schemas
Subschema objects (or booleans) are recognized by their use with known
applicator keywords or with location-reserving keywords such as
"$defs"
Section 8.2.4
that take one or more subschemas
as a value. These keywords may be "$defs" and the standard applicators
from this document, or extension keywords from a known vocabulary, or
implementation-specific custom keywords.
Multi-level structures of unknown keywords are capable of introducing
nested subschemas, which would be subject to the processing rules for
"$id". Therefore, having a reference target in such an unrecognized
structure cannot be reliably implemented, and the resulting behavior
is undefined. Similarly, a reference target under a known keyword,
for which the value is known not to be a schema, results in undefined
behavior in order to avoid burdening implementations with the need
to detect such targets.
These scenarios are analogous to fetching a schema over HTTP
but receiving a response with a Content-Type other than
application/schema+json. An implementation can certainly
try to interpret it as a schema, but the origin server
offered no guarantee that it actually is any such thing.
Therefore, interpreting it as such has security implications
and may produce unpredictable results.
Note that single-level custom keywords with identical syntax and
semantics to "$defs" do not allow for any intervening "$id" keywords,
and therefore will behave correctly under implementations that attempt
to use any reference target as a schema. However, this behavior is
implementation-specific and MUST NOT be relied upon for interoperability.
9.5.
Associating Instances and Schemas
9.5.1.
Usage for Hypermedia
JSON has been adopted widely by HTTP servers for automated APIs and robots. This
section describes how to enhance processing of JSON documents in a more RESTful
manner when used with protocols that support media types and
Web linking
RFC8288
9.5.1.1.
Linking to a Schema
It is RECOMMENDED that instances described by a schema provide a link to
a downloadable JSON Schema using the link relation "describedby", as defined by
Linked Data Protocol 1.0, section 8.1
W3C.REC-ldp-20150226
In HTTP, such links can be attached to any response using the
Link header
RFC8288
. An example of such a header would be:
Link: ; rel="describedby"
9.5.1.2.
Usage Over HTTP
When used for hypermedia systems over a network,
HTTP
RFC7231
is frequently the protocol of choice for
distributing schemas. Misbehaving clients can pose problems for server
maintainers if they pull a schema over the network more frequently than
necessary, when it's instead possible to cache a schema for a long period of
time.
HTTP servers SHOULD set long-lived caching headers on JSON Schemas.
HTTP clients SHOULD observe caching headers and not re-request documents within
their freshness period.
Distributed systems SHOULD make use of a shared cache and/or caching proxy.
Clients SHOULD set or prepend a User-Agent header specific to the JSON Schema
implementation or software product. Since symbols are listed in decreasing order
of significance, the JSON Schema library name/version should precede the more
generic HTTP library name (if any). For example:
User-Agent: product-name/5.4.1 so-cool-json-schema/1.0.2 curl/7.43.0
Clients SHOULD be able to make requests with a "From" header so that server
operators can contact the owner of a potentially misbehaving script.
10.
A Vocabulary for Applying Subschemas
This section defines a vocabulary of applicator keywords that
are RECOMMENDED for use as the basis of other vocabularies.
Meta-schemas that do not use "$vocabulary" SHOULD be considered to
require this vocabulary as if its URI were present with a value of true.
The current URI for this vocabulary, known as the Applicator vocabulary, is:
.
The current URI for the corresponding meta-schema is:
10.1.
Keyword Independence
Schema keywords typically operate independently, without
affecting each other's outcomes.
For schema author convenience, there are some exceptions among the
keywords in this vocabulary:
"additionalProperties", whose behavior is defined in terms of
"properties" and "patternProperties"
"items", whose behavior is defined in terms of "prefixItems"
"contains", whose behavior is affected by the presence and value of
"minContains", in the Validation vocabulary
10.2.
Keywords for Applying Subschemas in Place
These keywords apply subschemas to the same location in the instance
as the parent schema is being applied. They allow combining
or modifying the subschema results in various ways.
Subschemas of these keywords evaluate the instance completely independently
such that the results of one such subschema MUST NOT impact the results of sibling
subschemas. Therefore subschemas may be applied in
any order.
10.2.1.
Keywords for Applying Subschemas With Logic
These keywords correspond to logical operators for combining or modifying
the boolean assertion results of the subschemas. They have no direct
impact on annotation collection, although they enable the same annotation
keyword to be applied to an instance location with different values.
Annotation keywords define their own rules for combining such values.
10.2.1.1.
allOf
This keyword's value MUST be a non-empty array.
Each item of the array MUST be a valid JSON Schema.
An instance validates successfully against this keyword if it validates
successfully against all schemas defined by this keyword's value.
10.2.1.2.
anyOf
This keyword's value MUST be a non-empty array.
Each item of the array MUST be a valid JSON Schema.
An instance validates successfully against this keyword if it validates
successfully against at least one schema defined by this keyword's value.
Note that when annotations are being collected, all subschemas MUST
be examined so that annotations are collected from each subschema
that validates successfully.
10.2.1.3.
oneOf
This keyword's value MUST be a non-empty array.
Each item of the array MUST be a valid JSON Schema.
An instance validates successfully against this keyword if it validates
successfully against exactly one schema defined by this keyword's value.
10.2.1.4.
not
This keyword's value MUST be a valid JSON Schema.
An instance is valid against this keyword if it fails to validate
successfully against the schema defined by this keyword.
10.2.2.
Keywords for Applying Subschemas Conditionally
Three of these keywords work together to implement conditional
application of a subschema based on the outcome of another subschema.
The fourth is a shortcut for a specific conditional case.
"if", "then", and "else" MUST NOT interact with each other across
subschema boundaries. In other words, an "if" in one
branch of an "allOf" MUST NOT have an impact on a "then"
or "else" in another branch.
There is no default behavior for "if", "then", or "else"
when they are not present. In particular, they MUST NOT
be treated as if present with an empty schema, and when
"if" is not present, both "then" and "else" MUST be
entirely ignored.
10.2.2.1.
if
This keyword's value MUST be a valid JSON Schema.
This validation outcome of this keyword's subschema
has no direct effect on the overall validation
result. Rather, it controls which of the "then"
or "else" keywords are evaluated.
Instances that successfully validate against this
keyword's subschema MUST also be valid against
the subschema value of the "then" keyword, if
present.
Instances that fail to validate against this
keyword's subschema MUST also be valid against
the subschema value of the "else" keyword, if
present.
If
annotations
Section 7.7
are being collected, they are collected from this
keyword's subschema in the usual way, including when
the keyword is present without either "then" or "else".
10.2.2.2.
then
This keyword's value MUST be a valid JSON Schema.
When "if" is present, and the instance successfully
validates against its subschema, then validation
succeeds against this keyword if the instance also
successfully validates against this keyword's subschema.
This keyword has no effect when "if" is absent, or
when the instance fails to validate against its
subschema. Implementations MUST NOT evaluate
the instance against this keyword, for either validation
or annotation collection purposes, in such cases.
10.2.2.3.
else
This keyword's value MUST be a valid JSON Schema.
When "if" is present, and the instance fails to
validate against its subschema, then validation
succeeds against this keyword if the instance
successfully validates against this keyword's subschema.
This keyword has no effect when "if" is absent, or
when the instance successfully validates against its
subschema. Implementations MUST NOT evaluate
the instance against this keyword, for either validation
or annotation collection purposes, in such cases.
10.2.2.4.
dependentSchemas
This keyword specifies subschemas that are evaluated if the instance
is an object and contains a certain property.
This keyword's value MUST be an object.
Each value in the object MUST be a valid JSON Schema.
If the object key is a property in the instance, the entire
instance must validate against the subschema. Its use is
dependent on the presence of the property.
Omitting this keyword has the same behavior as an empty object.
10.3.
Keywords for Applying Subschemas to Child Instances
Each of these keywords defines a rule for applying its
subschema(s) to child instances, specifically object
properties and array items, and combining their results.
10.3.1.
Keywords for Applying Subschemas to Arrays
10.3.1.1.
prefixItems
The value of "prefixItems" MUST be a non-empty array of valid JSON Schemas.
Validation succeeds if each element of the instance validates
against the schema at the same position, if any. This keyword
does not constrain the length of the array. If the array is longer
than this keyword's value, this keyword validates only the
prefix of matching length.
This keyword produces an annotation value which is the largest
index to which this keyword applied a subschema. The value
MAY be a boolean true if a subschema was applied to every
index of the instance, such as is produced by the "items" keyword.
This annotation affects the behavior of "items" and "unevaluatedItems".
Omitting this keyword has the same assertion behavior as
an empty array.
10.3.1.2.
items
The value of "items" MUST be a valid JSON Schema.
This keyword applies its subschema to all instance elements
at indexes greater than the length of the "prefixItems" array
in the same schema object, as reported by the annotation result
of that "prefixItems" keyword. If no such annotation
result exists, "items" applies its subschema to all instance
array elements.
Note that the behavior of "items" without "prefixItems" is
identical to that of the schema form of "items" in prior drafts.
When "prefixItems" is present, the behavior of "items" is
identical to the former "additionalItems" keyword.
If the "items" subschema is applied to any
positions within the instance array, it produces an
annotation result of boolean true, indicating that all remaining array
elements have been evaluated against this keyword's subschema.
This annotation affects the behavior of "unevaluatedItems" in the
Unevaluated vocabulary.
Omitting this keyword has the same assertion behavior as
an empty schema.
Implementations MAY choose to implement or optimize this keyword
in another way that produces the same effect, such as by directly
checking for the presence and size of a "prefixItems" array.
Implementations that do not support annotation collection MUST do so.
10.3.1.3.
contains
The value of this keyword MUST be a valid JSON Schema.
An array instance is valid against "contains" if at least one of
its elements is valid against the given schema,
except when "minContains" is present and has a value of 0, in which
case an array instance MUST be considered valid against the "contains" keyword,
even if none of its elements is valid against the given schema.
This keyword produces an annotation value which is an array of
the indexes to which this keyword validates successfully when applying
its subschema, in ascending order. The value MAY be a boolean "true" if
the subschema validates successfully when applied to every index of the
instance. The annotation MUST be present if the instance array to which
this keyword's schema applies is empty.
This annotation affects the behavior of "unevaluatedItems" in the
Unevaluated vocabulary, and MAY also be used to implement the
"minContains" and "maxContains" keywords in the Validation vocabulary.
The subschema MUST be applied to every array element even after the first
match has been found, in order to collect annotations for use by other
keywords. This is to ensure that all possible annotations are collected.
10.3.2.
Keywords for Applying Subschemas to Objects
10.3.2.1.
properties
The value of "properties" MUST be an object.
Each value of this object MUST be a valid JSON Schema.
Validation succeeds if, for each name that appears in both
the instance and as a name within this keyword's value, the child
instance for that name successfully validates against the
corresponding schema.
The annotation result of this keyword is the set of instance
property names matched by this keyword.
This annotation affects the behavior of "additionalProperties" (in
this vocabulary) and "unevaluatedProperties" in the Unevaluated vocabulary.
Omitting this keyword has the same assertion behavior as
an empty object.
10.3.2.2.
patternProperties
The value of "patternProperties" MUST be an object. Each property name
of this object SHOULD be a valid regular expression, according to the
ECMA-262 regular expression dialect. Each property value of this object
MUST be a valid JSON Schema.
Validation succeeds if, for each instance name that matches any
regular expressions that appear as a property name in this keyword's value,
the child instance for that name successfully validates against each
schema that corresponds to a matching regular expression.
The annotation result of this keyword is the set of instance
property names matched by this keyword.
This annotation affects the behavior of "additionalProperties" (in this
vocabulary) and "unevaluatedProperties" (in the Unevaluated vocabulary).
Omitting this keyword has the same assertion behavior as
an empty object.
10.3.2.3.
additionalProperties
The value of "additionalProperties" MUST be a valid JSON Schema.
The behavior of this keyword depends on the presence and
annotation results of "properties" and "patternProperties"
within the same schema object.
Validation with "additionalProperties" applies only to the child
values of instance names that do not appear in the annotation
results of either "properties" or "patternProperties".
For all such properties, validation succeeds if the child instance
validates against the "additionalProperties" schema.
The annotation result of this keyword is the set of instance
property names validated by this keyword's subschema.
This annotation affects the behavior of "unevaluatedProperties"
in the Unevaluated vocabulary.
Omitting this keyword has the same assertion behavior as
an empty schema.
Implementations MAY choose to implement or optimize this keyword
in another way that produces the same effect, such as by directly
checking the names in "properties" and the patterns in
"patternProperties" against the instance property set.
Implementations that do not support annotation collection MUST do so.
In defining this option, it seems there is the potential for
ambiguity in the output format. The ambiguity does not affect validation results,
but it does affect the resulting output format.
The ambiguity allows for multiple valid output results depending on whether annotations
are used or a solution that "produces the same effect" as draft-07. It is understood
that annotations from failing schemas are dropped.
See our
[Decision Record](https://github.com/json-schema-org/json-schema-spec/tree/HEAD/adr/2022-04-08-cref-for-ambiguity-and-fix-later-gh-spec-issue-1172.md)
for further details.
10.3.2.4.
propertyNames
The value of "propertyNames" MUST be a valid JSON Schema.
If the instance is an object, this keyword validates if every property name in
the instance validates against the provided schema.
Note the property name that the schema is testing will always be a string.
Omitting this keyword has the same behavior as an empty schema.
11.
A Vocabulary for Unevaluated Locations
The purpose of these keywords is to enable schema authors to apply
subschemas to array items or object properties that have not been
successfully evaluated against any dynamic-scope subschema of any
adjacent keywords.
These instance items or properties may have been unsuccessfully evaluated
against one or more adjacent keyword subschemas, such as when an assertion
in a branch of an "anyOf" fails. Such failed evaluations are not considered
to contribute to whether or not the item or property has been evaluated.
Only successful evaluations are considered.
If an item in an array or an object property is "successfully evaluated", it
is logically considered to be valid in terms of the representation of the
object or array that's expected. For example if a subschema represents a car,
which requires between 2-4 wheels, and the value of "wheels" is 6, the instance
object is not "evaluated" to be a car, and the "wheels" property is considered
"unevaluated (successfully as a known thing)", and does not retain any annotations.
Recall that adjacent keywords are keywords within the same schema object,
and that the dynamic-scope subschemas include reference targets as well as
lexical subschemas.
The behavior of these keywords depend on the annotation results of
adjacent keywords that apply to the instance location being validated.
Meta-schemas that do not use "$vocabulary" SHOULD be considered to
require this vocabulary as if its URI were present with a value of true.
The current URI for this vocabulary, known as the Unevaluated Applicator
vocabulary, is:
.
The current URI for the corresponding meta-schema is:
11.1.
Keyword Independence
Schema keywords typically operate independently, without
affecting each other's outcomes. However, the keywords in this
vocabulary are notable exceptions:
"unevaluatedItems", whose behavior is defined in terms of annotations
from "prefixItems", "items", "contains", and itself
"unevaluatedProperties", whose behavior is defined in terms of
annotations from "properties", "patternProperties",
"additionalProperties" and itself
11.2.
unevaluatedItems
The value of "unevaluatedItems" MUST be a valid JSON Schema.
The behavior of this keyword depends on the annotation results of
adjacent keywords that apply to the instance location being validated.
Specifically, the annotations from "prefixItems", "items", and "contains",
which can come from those keywords when they are adjacent to the
"unevaluatedItems" keyword. Those three annotations, as well as
"unevaluatedItems", can also result from any and all adjacent
in-place applicator
Section 10.2
keywords.
This includes but is not limited to the in-place applicators
defined in this document.
If no relevant annotations are present, the "unevaluatedItems"
subschema MUST be applied to all locations in the array.
If a boolean true value is present from any of the relevant annotations,
"unevaluatedItems" MUST be ignored. Otherwise, the subschema
MUST be applied to any index greater than the largest annotation
value for "prefixItems", which does not appear in any annotation
value for "contains".
This means that "prefixItems", "items", "contains", and all in-place
applicators MUST be evaluated before this keyword can be evaluated.
Authors of extension keywords MUST NOT define an in-place applicator
that would need to be evaluated after this keyword.
If the "unevaluatedItems" subschema is applied to any
positions within the instance array, it produces an
annotation result of boolean true, analogous to the
behavior of "items".
This annotation affects the behavior of "unevaluatedItems" in parent schemas.
Omitting this keyword has the same assertion behavior as
an empty schema.
11.3.
unevaluatedProperties
The value of "unevaluatedProperties" MUST be a valid JSON Schema.
The behavior of this keyword depends on the annotation results of
adjacent keywords that apply to the instance location being validated.
Specifically, the annotations from "properties", "patternProperties",
and "additionalProperties", which can come from those keywords when
they are adjacent to the "unevaluatedProperties" keyword. Those
three annotations, as well as "unevaluatedProperties", can also
result from any and all adjacent
in-place applicator
Section 10.2
keywords.
This includes but is not limited to the in-place applicators
defined in this document.
Validation with "unevaluatedProperties" applies only to the child
values of instance names that do not appear in the "properties",
"patternProperties", "additionalProperties", or
"unevaluatedProperties" annotation results that apply to the
instance location being validated.
For all such properties, validation succeeds if the child instance
validates against the "unevaluatedProperties" schema.
This means that "properties", "patternProperties", "additionalProperties",
and all in-place applicators MUST be evaluated before this keyword can
be evaluated. Authors of extension keywords MUST NOT define an in-place
applicator that would need to be evaluated after this keyword.
The annotation result of this keyword is the set of instance
property names validated by this keyword's subschema.
This annotation affects the behavior of "unevaluatedProperties" in parent schemas.
Omitting this keyword has the same assertion behavior as
an empty schema.
12.
Output Formatting
JSON Schema is defined to be platform-independent. As such, to increase compatibility
across platforms, implementations SHOULD conform to a standard validation output
format. This section describes the minimum requirements that consumers will need to
properly interpret validation results.
12.1.
Format
JSON Schema output is defined using the JSON Schema data instance model as described
in section 4.2.1. Implementations MAY deviate from this as supported by their
specific languages and platforms, however it is RECOMMENDED that the output be
convertible to the JSON format defined herein via serialization or other means.
12.2.
Output Formats
This specification defines four output formats. See the "Output Structure"
section for the requirements of each format.
Flag - A boolean which simply indicates the overall validation result
with no further details.
Basic - Provides validation information in a flat list structure.
Detailed - Provides validation information in a condensed hierarchical
structure based on the structure of the schema.
Verbose - Provides validation information in an uncondensed hierarchical
structure that matches the exact structure of the schema.
An implementation SHOULD provide at least one of the "flag", "basic", or "detailed"
format and MAY provide the "verbose" format. If it provides one or more of the
"detailed" or "verbose" formats, it MUST also provide the "flag" format.
Implementations SHOULD specify in their documentation which formats they support.
12.3.
Minimum Information
Beyond the simplistic "flag" output, additional information is useful to aid in
debugging a schema or instance. Each sub-result SHOULD contain the information
contained within this section at a minimum.
A single object that contains all of these components is considered an
output unit.
Implementations MAY elect to provide additional information.
12.3.1.
Keyword Relative Location
The relative location of the validating keyword that follows the validation
path. The value MUST be expressed as a JSON Pointer, and it MUST include
any by-reference applicators such as "$ref" or "$dynamicRef".
/properties/width/$ref/minimum
Note that this pointer may not be resolvable by the normal JSON Pointer process
due to the inclusion of these by-reference applicator keywords.
The JSON key for this information is "keywordLocation".
12.3.2.
Keyword Absolute Location
The absolute, dereferenced location of the validating keyword. The value MUST
be expressed as a full URI using the canonical URI of the relevant schema resource
with a JSON Pointer fragment, and it MUST NOT include by-reference applicators
such as "$ref" or "$dynamicRef" as non-terminal path components.
It MAY end in such keywords if the error or annotation is for that
keyword, such as an unresolvable reference.
Note that "absolute" here is in the sense of "absolute filesystem path"
(meaning the complete location) rather than the "absolute-URI"
terminology from RFC 3986 (meaning with scheme but without fragment).
Keyword absolute locations will have a fragment in order to
identify the keyword.
This information MAY be omitted only if either the dynamic scope did not pass
over a reference or if the schema does not declare an absolute URI as its "$id".
The JSON key for this information is "absoluteKeywordLocation".
12.3.3.
Instance Location
The location of the JSON value within the instance being validated. The
value MUST be expressed as a JSON Pointer.
The JSON key for this information is "instanceLocation".
12.3.4.
Error or Annotation
The error or annotation that is produced by the validation.
For errors, the specific wording for the message is not defined by this
specification. Implementations will need to provide this.
For annotations, each keyword that produces an annotation specifies its
format. By default, it is the keyword's value.
The JSON key for failed validations is "error"; for successful validations
it is "annotation".
12.3.5.
Nested Results
For the two hierarchical structures, this property will hold nested errors
and annotations.
The JSON key for nested results in failed validations is "errors"; for
successful validations it is "annotations". Note the plural forms, as
a keyword with nested results can also have a local error or annotation.
12.4.
Output Structure
The output MUST be an object containing a boolean property named "valid". When
additional information about the result is required, the output MUST also contain
"errors" or "annotations" as described below.
"valid" - a boolean value indicating the overall validation success or
failure
"errors" - the collection of errors or annotations produced by a failed
validation
"annotations" - the collection of errors or annotations produced by a
successful validation
For these examples, the following schema and instance will be used.
"$id": "https://example.com/polygon",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$defs": {
"point": {
"type": "object",
"properties": {
"x": { "type": "number" },
"y": { "type": "number" }
},
"additionalProperties": false,
"required": [ "x", "y" ]
},
"type": "array",
"items": { "$ref": "#/$defs/point" },
"minItems": 3

"x": 2.5,
"y": 1.3
},
"x": 1,
"z": 6.7
This instance will fail validation and produce errors, but it's trivial to deduce
examples for passing schemas that produce annotations.
Specifically, the errors it will produce are:
The second object is missing a "y" property.
The second object has a disallowed "z" property.
There are only two objects, but three are required.
Note that the error message wording as depicted in these examples is not a
requirement of this specification. Implementations SHOULD craft error messages
tailored for their audience or provide a templating mechanism that allows their
users to craft their own messages.
12.4.1.
Flag
In the simplest case, merely the boolean result for the "valid" valid property
needs to be fulfilled.
"valid": false
Because no errors or annotations are returned with this format, it is
RECOMMENDED that implementations use short-circuiting logic to return
failure or success as soon as the outcome can be determined. For example,
if an "anyOf" keyword contains five sub-schemas, and the second one
passes, there is no need to check the other three. The logic can simply
return with success.
12.4.2.
Basic
The "Basic" structure is a flat list of output units.
"valid": false,
"errors": [
"keywordLocation": "",
"instanceLocation": "",
"error": "A subschema had errors."
},
"keywordLocation": "/items/$ref",
"absoluteKeywordLocation":
"https://example.com/polygon#/$defs/point",
"instanceLocation": "/1",
"error": "A subschema had errors."
},
"keywordLocation": "/items/$ref/required",
"absoluteKeywordLocation":
"https://example.com/polygon#/$defs/point/required",
"instanceLocation": "/1",
"error": "Required property 'y' not found."
},
"keywordLocation": "/items/$ref/additionalProperties",
"absoluteKeywordLocation":
"https://example.com/polygon#/$defs/point/additionalProperties",
"instanceLocation": "/1/z",
"error": "Additional property 'z' found but was invalid."
},
"keywordLocation": "/minItems",
"instanceLocation": "",
"error": "Expected at least 3 items but found 2"
12.4.3.
Detailed
The "Detailed" structure is based on the schema and can be more readable
for both humans and machines. Having the structure organized this way makes
associations between the errors more apparent. For example, the fact that
the missing "y" property and the extra "z" property both stem from the same
location in the instance is not immediately obvious in the "Basic" structure.
In a hierarchy, the correlation is more easily identified.
The following rules govern the construction of the results object:
All applicator keywords ("*Of", "$ref", "if"/"then"/"else", etc.) require
a node.
Nodes that have no children are removed.
Nodes that have a single child are replaced by the child.
Branch nodes do not require an error message or an annotation.
"valid": false,
"keywordLocation": "",
"instanceLocation": "",
"errors": [
"valid": false,
"keywordLocation": "/items/$ref",
"absoluteKeywordLocation":
"https://example.com/polygon#/$defs/point",
"instanceLocation": "/1",
"errors": [
"valid": false,
"keywordLocation": "/items/$ref/required",
"absoluteKeywordLocation":
"https://example.com/polygon#/$defs/point/required",
"instanceLocation": "/1",
"error": "Required property 'y' not found."
},
"valid": false,
"keywordLocation": "/items/$ref/additionalProperties",
"absoluteKeywordLocation":
"https://example.com/polygon#/$defs/point/additionalProperties",
"instanceLocation": "/1/z",
"error": "Additional property 'z' found but was invalid."
},
"valid": false,
"keywordLocation": "/minItems",
"instanceLocation": "",
"error": "Expected at least 3 items but found 2"
12.4.4.
Verbose
The "Verbose" structure is a fully realized hierarchy that exactly matches
that of the schema. This structure has applications in form generation and
validation where the error's location is important.
The primary difference between this and the "Detailed" structure is that
all results are returned. This includes sub-schema validation results that
would otherwise be removed (e.g. annotations for failed validations,
successful validations inside a `not` keyword, etc.). Because of this, it
is RECOMMENDED that each node also carry a `valid` property to indicate the
validation result for that node.
Because this output structure can be quite large, a smaller example is given
here for brevity. The URI of the full output structure of the example above is:
// schema
"$id": "https://example.com/polygon",
"$schema": "https://json-schema.org/draft/2020-12/schema",
"type": "object",
"properties": {
"validProp": true,
},
"additionalProperties": false

// instance
"validProp": 5,
"disallowedProp": "value"

// result
"valid": false,
"keywordLocation": "",
"instanceLocation": "",
"errors": [
"valid": true,
"keywordLocation": "/type",
"instanceLocation": ""
},
"valid": true,
"keywordLocation": "/properties",
"instanceLocation": ""
},
"valid": false,
"keywordLocation": "/additionalProperties",
"instanceLocation": "",
"errors": [
"valid": false,
"keywordLocation": "/additionalProperties",
"instanceLocation": "/disallowedProp",
"error": "Additional property 'disallowedProp' found but was invalid."
12.4.5.
Output validation schemas
For convenience, JSON Schema has been provided to validate output generated
by implementations. Its URI is:
13.
Security Considerations
Both schemas and instances are JSON values. As such, all security considerations
defined in
RFC 8259
RFC8259
apply.
Instances and schemas are both frequently written by untrusted third parties, to be
deployed on public Internet servers.
Validators should take care that the parsing and validating against schemas does not consume excessive
system resources.
Validators MUST NOT fall into an infinite loop.
A malicious party could cause an implementation to repeatedly collect a copy
of a very large value as an annotation. Implementations SHOULD guard against
excessive consumption of system resources in such a scenario.
Servers MUST ensure that malicious parties cannot change the functionality of
existing schemas by uploading a schema with a pre-existing or very similar "$id".
Individual JSON Schema vocabularies are liable to also have their own security
considerations. Consult the respective specifications for more information.
Schema authors should take care with "$comment" contents, as a malicious
implementation can display them to end-users in violation of a spec, or
fail to strip them if such behavior is expected.
A malicious schema author could place executable code or other dangerous
material within a "$comment". Implementations MUST NOT parse or otherwise
take action based on "$comment" contents.
14.
IANA Considerations
14.1.
application/schema+json
The proposed MIME media type for JSON Schema is defined as follows:
Type name: application
Subtype name: schema+json
Required parameters: N/A
Encoding considerations: Encoding considerations are
identical to those specified for the "application/json"
media type. See
JSON
RFC8259
Security considerations: See Section
13
above.
Interoperability considerations: See Sections
6.2
6.3
, and
6.4
above.
Fragment identifier considerations: See Section
14.2.
application/schema-instance+json
The proposed MIME media type for JSON Schema Instances that require
a JSON Schema-specific media type is defined as follows:
Type name: application
Subtype name: schema-instance+json
Required parameters: N/A
Encoding considerations: Encoding considerations are
identical to those specified for the "application/json"
media type. See
JSON
RFC8259
Security considerations: See Section
13
above.
Interoperability considerations: See Sections
6.2
6.3
, and
6.4
above.
Fragment identifier considerations: See Section
15.
References
15.1.
Normative References
[RFC2119]
Bradner, S.
"Key words for use in RFCs to Indicate Requirement Levels"
BCP 14
RFC 2119
DOI 10.17487/RFC2119
March 1997
[RFC3986]
Berners-Lee, T.
Fielding, R.
, and
L. Masinter
"Uniform Resource Identifier (URI): Generic Syntax"
STD 66
RFC 3986
DOI 10.17487/RFC3986
January 2005
[RFC6839]
Hansen, T.
and
A. Melnikov
"Additional Media Type Structured Syntax Suffixes"
RFC 6839
DOI 10.17487/RFC6839
January 2013
[RFC6901]
Bryan, P., Ed.
Zyp, K.
, and
M. Nottingham, Ed.
"JavaScript Object Notation (JSON) Pointer"
RFC 6901
DOI 10.17487/RFC6901
April 2013
[RFC8259]
Bray, T., Ed.
"The JavaScript Object Notation (JSON) Data Interchange Format"
STD 90
RFC 8259
DOI 10.17487/RFC8259
December 2017
[W3C.REC-ldp-20150226]
Speicher, S.
Arwe, J.
, and
A. Malhotra
"Linked Data Platform 1.0"
World Wide Web Consortium Recommendation REC-ldp-20150226
26 February 2015
[ecma262]
"ECMA-262, 11th edition specification"
June 2020
15.2.
Informative References
[RFC6596]
Ohye, M.
and
J. Kupke
"The Canonical Link Relation"
RFC 6596
DOI 10.17487/RFC6596
April 2012
[RFC7049]
Bormann, C.
and
P. Hoffman
"Concise Binary Object Representation (CBOR)"
RFC 7049
DOI 10.17487/RFC7049
October 2013
[RFC7231]
Fielding, R., Ed.
and
J. Reschke, Ed.
"Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content"
RFC 7231
DOI 10.17487/RFC7231
June 2014
[RFC8288]
Nottingham, M.
"Web Linking"
RFC 8288
DOI 10.17487/RFC8288
October 2017
[W3C.WD-fragid-best-practices-20121025]
Tennison, J.
"Best Practices for Fragment Identifiers and Media Type Definitions"
World Wide Web Consortium WD WD-fragid-best-practices-20121025
25 October 2012
[json-schema-validation]
Wright, A.
Andrews, H.
, and
B. Hutton
"JSON Schema Validation: A Vocabulary for Structural Validation of JSON"
Work in Progress
Internet-Draft, draft-bhutton-json-schema-validation-01
June 2022
[json-hyper-schema]
Andrews, H.
and
A. Wright
"JSON Hyper-Schema: A Vocabulary for Hypermedia Annotation of JSON"
Work in Progress
Internet-Draft, draft-handrews-json-schema-hyperschema-02
November 2017
[xml-names]
Bray, T., Ed.
Hollander, D., Ed.
Layman, A., Ed.
, and
R. Tobin, Ed.
"Namespaces in XML 1.1 (Second Edition)"
August 2006
Appendix A.
Schema identification examples
Consider the following schema, which shows "$id" being used to identify
both the root schema and various subschemas, and "$anchor" being used
to define plain name fragment identifiers.
"$id": "https://example.com/root.json",
"$defs": {
"A": { "$anchor": "foo" },
"B": {
"$id": "other.json",
"$defs": {
"X": { "$anchor": "bar" },
"Y": {
"$id": "t/inner.json",
"$anchor": "bar"
},
"C": {
"$id": "urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f"
The schemas at the following URI-encoded
JSON
Pointers
RFC6901
(relative to the root schema) have the following
base URIs, and are identifiable by any listed URI in accordance with
sections
and
9.2.1
above.
# (document root)
canonical (and base) URI
canonical resource URI plus pointer fragment
#/$defs/A
base URI
canonical resource URI plus plain fragment
canonical resource URI plus pointer fragment
#/$defs/B
canonical (and base) URI
canonical resource URI plus pointer fragment
base URI of enclosing (root.json) resource plus fragment
#/$defs/B/$defs/X
base URI
canonical resource URI plus plain fragment
canonical resource URI plus pointer fragment
base URI of enclosing (root.json) resource plus fragment
#/$defs/B/$defs/Y
canonical (and base) URI
canonical URI plus plain fragment
canonical URI plus pointer fragment
base URI of enclosing (other.json) resource plus fragment
base URI of enclosing (root.json) resource plus fragment
#/$defs/C
canonical (and base) URI
urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f
canonical URI plus pointer fragment
urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f#
base URI of enclosing (root.json) resource plus fragment
Note: The fragment part of the URI does not make it canonical or non-canonical,
rather, the base URI used (as part of the full URI with any fragment) is what
determines the canonical nature of the resulting full URI.
Multiple "canonical" URIs? We Acknowledge this is potentially confusing, and
direct you to read the CREF located in the
JSON Pointer fragments and embedded schema resources
Section 9.2.1
section for futher comments.
Appendix B.
Manipulating schema documents and references
Various tools have been created to rearrange schema documents
based on how and where references ("$ref") appear. This appendix discusses
which use cases and actions are compliant with this specification.
B.1.
Bundling schema resources into a single document
A set of schema resources intended for use together can be organized
with each in its own schema document, all in the same schema document,
or any granularity of document grouping in between.
Numerous tools exist to perform various sorts of reference removal.
A common case of this is producing a single file where all references
can be resolved within that file. This is typically done to simplify
distribution, or to simplify coding so that various invocations
of JSON Schema libraries do not have to keep track of and load
a large number of resources.
This transformation can be safely and reversibly done as long as
all static references (e.g. "$ref") use URI-references that resolve
to URIs using the canonical resource URI as the base, and all schema
resources have an absolute-URI as the "$id" in their root schema.
With these conditions met, each external resource can be copied
under "$defs", without breaking any references among the resources'
schema objects, and without changing any aspect of validation or
annotation results. The names of the schemas under "$defs" do
not affect behavior, assuming they are each unique, as they
do not appear in the canonical URIs for the embedded resources.
B.2.
Reference removal is not always safe
Attempting to remove all references and produce a single schema document does not,
in all cases, produce a schema with identical behavior to the original form.
Since "$ref" is now treated like any other keyword, with other keywords allowed
in the same schema objects, fully supporting non-recursive "$ref" removal in
all cases can require relatively complex schema manipulations. It is beyond
the scope of this specification to determine or provide a set of safe "$ref"
removal transformations, as they depend not only on the schema structure
but also on the intended usage.
Appendix C.
Example of recursive schema extension
Consider the following two schemas describing a simple
recursive tree structure, where each node in the tree
can have a "data" field of any type. The first schema
allows and ignores other instance properties. The second is
more strict and only allows the "data" and "children" properties.
An example instance with "data" misspelled as "daat" is also shown.
// tree schema, extensible
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$id": "https://example.com/tree",
"$dynamicAnchor": "node",

"type": "object",
"properties": {
"data": true,
"children": {
"type": "array",
"items": {
"$dynamicRef": "#node"

// strict-tree schema, guards against misspelled properties
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$id": "https://example.com/strict-tree",
"$dynamicAnchor": "node",

"$ref": "tree",
"unevaluatedProperties": false

// instance with misspelled field
"children": [ { "daat": 1 } ]
When we load these two schemas, we will notice the "$dynamicAnchor"
named "node" (note the lack of "#" as this is just the name)
present in each, resulting in the following full schema URIs:
"https://example.com/tree#node"
"https://example.com/strict-tree#node"
In addition, JSON Schema implementations keep track of the fact
that these fragments were created with "$dynamicAnchor".
If we apply the "strict-tree" schema to the instance, we will follow
the "$ref" to the "tree" schema, examine its "children" subschema,
and find the "$dynamicRef": to "#node" (note the "#" for URI fragment syntax)
in its "items" subschema. That reference resolves to
"https://example.com/tree#node", which is a URI with a fragment
created by "$dynamicAnchor". Therefore we must examine the dynamic
scope before following the reference.
At this point, the dynamic path is
"#/$ref/properties/children/items/$dynamicRef", with a dynamic scope
containing (from the outermost scope to the innermost):
"https://example.com/strict-tree#"
"https://example.com/tree#"
"https://example.com/tree#/properties/children"
"https://example.com/tree#/properties/children/items"
Since we are looking for a plain name fragment, which can be
defined anywhere within a schema resource, the JSON Pointer fragments
are irrelevant to this check. That means that we can remove those
fragments and eliminate consecutive duplicates, producing:
"https://example.com/strict-tree"
"https://example.com/tree"
In this case, the outermost resource also has a "node" fragment
defined by "$dynamicAnchor". Therefore instead of resolving the
"$dynamicRef" to "https://example.com/tree#node", we resolve it to
"https://example.com/strict-tree#node".
This way, the recursion in the "tree" schema recurses to the root
of "strict-tree", instead of only applying "strict-tree" to the
instance root, but applying "tree" to instance children.
This example shows both "$dynamicAnchor"s in the same place
in each schema, specifically the resource root schema.
Since plain-name fragments are independent of the JSON structure,
this would work just as well if one or both of the node schema objects
were moved under "$defs". It is the matching "$dynamicAnchor" values
which tell us how to resolve the dynamic reference, not any sort of
correlation in JSON structure.
Appendix D.
Working with vocabularies
D.1.
Best practices for vocabulary and meta-schema authors
Vocabulary authors should
take care to avoid keyword name collisions if the vocabulary is intended
for broad use, and potentially combined with other vocabularies. JSON
Schema does not provide any formal namespacing system, but also does
not constrain keyword names, allowing for any number of namespacing
approaches.
Vocabularies may build on each other, such as by defining the behavior
of their keywords with respect to the behavior of keywords from another
vocabulary, or by using a keyword from another vocabulary with
a restricted or expanded set of acceptable values. Not all such
vocabulary re-use will result in a new vocabulary that is compatible
with the vocabulary on which it is built. Vocabulary authors should
clearly document what level of compatibility, if any, is expected.
Meta-schema authors should not use "$vocabulary" to combine multiple
vocabularies that define conflicting syntax or semantics for the same
keyword. As semantic conflicts are not generally detectable through
schema validation, implementations are not expected to detect such
conflicts. If conflicting vocabularies are declared, the resulting
behavior is undefined.
Vocabulary authors SHOULD provide a meta-schema that validates the
expected usage of the vocabulary's keywords on their own. Such meta-schemas
SHOULD not forbid additional keywords, and MUST not forbid any
keywords from the Core vocabulary.
It is recommended that meta-schema authors reference each vocabulary's
meta-schema using the
"allOf"
Section 10.2.1.1
keyword,
although other mechanisms for constructing the meta-schema may be
appropriate for certain use cases.
The recursive nature of meta-schemas makes the "$dynamicAnchor"
and "$dynamicRef" keywords particularly useful for extending
existing meta-schemas, as can be seen in the JSON Hyper-Schema meta-schema
which extends the Validation meta-schema.
Meta-schemas may impose additional constraints, including describing
keywords not present in any vocabulary, beyond what the meta-schemas
associated with the declared vocabularies describe. This allows for
restricting usage to a subset of a vocabulary, and for validating
locally defined keywords not intended for re-use.
However, meta-schemas should not contradict any vocabularies that
they declare, such as by requiring a different JSON type than
the vocabulary expects. The resulting behavior is undefined.
Meta-schemas intended for local use, with no need to test for
vocabulary support in arbitrary implementations, can safely omit
"$vocabulary" entirely.
D.2.
Example meta-schema with vocabulary declarations
This meta-schema explicitly declares both the Core and Applicator vocabularies,
together with an extension vocabulary, and combines their meta-schemas with
an "allOf". The extension vocabulary's meta-schema, which describes only the
keywords in that vocabulary, is shown after the main example meta-schema.
The main example meta-schema also restricts the usage of the Unevaluated
vocabulary by forbidding the keywords prefixed with "unevaluated", which
are particularly complex to implement. This does not change the semantics
or set of keywords defined by the other vocabularies. It just ensures
that schemas using this meta-schema that attempt to use the keywords
prefixed with "unevaluated" will fail validation against this meta-schema.
Finally, this meta-schema describes the syntax of a keyword, "localKeyword",
that is not part of any vocabulary. Presumably, the implementors and users
of this meta-schema will understand the semantics of "localKeyword".
JSON Schema does not define any mechanism for expressing keyword semantics
outside of vocabularies, making them unsuitable for use except in a
specific environment in which they are understood.
This meta-schema combines several vocabularies for general use.
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$id": "https://example.com/meta/general-use-example",
"$dynamicAnchor": "meta",
"$vocabulary": {
"https://json-schema.org/draft/2020-12/vocab/core": true,
"https://json-schema.org/draft/2020-12/vocab/applicator": true,
"https://json-schema.org/draft/2020-12/vocab/validation": true,
"https://example.com/vocab/example-vocab": true
},
"allOf": [
{"$ref": "https://json-schema.org/draft/2020-12/meta/core"},
{"$ref": "https://json-schema.org/draft/2020-12/meta/applicator"},
{"$ref": "https://json-schema.org/draft/2020-12/meta/validation"},
{"$ref": "https://example.com/meta/example-vocab"}
],
"patternProperties": {
"^unevaluated": false
},
"properties": {
"localKeyword": {
"$comment": "Not in vocabulary, but validated if used",
"type": "string"
This meta-schema describes only a single extension vocabulary.
"$schema": "https://json-schema.org/draft/2020-12/schema",
"$id": "https://example.com/meta/example-vocab",
"$dynamicAnchor": "meta",
"$vocabulary": {
"https://example.com/vocab/example-vocab": true,
},
"type": ["object", "boolean"],
"properties": {
"minDate": {
"type": "string",
"pattern": "\d\d\d\d-\d\d-\d\d",
"format": "date",
As shown above, even though each of the single-vocabulary meta-schemas
referenced in the general-use meta-schema's "allOf" declares its
corresponding vocabulary, this new meta-schema must re-declare them.
The standard meta-schemas that combine all vocabularies defined by
the Core and Validation specification, and that combine all vocabularies
defined by those specifications as well as the Hyper-Schema specification,
demonstrate additional complex combinations. These URIs for these
meta-schemas may be found in the Validation and Hyper-Schema specifications,
respectively.
While the general-use meta-schema can validate the syntax of "minDate",
it is the vocabulary that defines the logic behind the semantic meaning
of "minDate". Without an understanding of the semantics (in this example,
that the instance value must be a date equal to or after the date
provided as the keyword's value in the schema), an implementation can
only validate the syntactic usage. In this case, that means validating
that it is a date-formatted string (using "pattern" to ensure that it is
validated even when "format" functions purely as an annotation, as explained
in the
Validation specification
json-schema-validation
Appendix E.
References and generative use cases
While the presence of references is expected to be transparent
to validation results, generative use cases such as code generators
and UI renderers often consider references to be semantically significant.
To make such use case-specific semantics explicit, the best practice
is to create an annotation keyword for use in the same
schema object alongside of a reference keyword such as "$ref".
For example, here is a hypothetical keyword for determining
whether a code generator should consider the reference
target to be a distinct class, and how those classes are related.
Note that this example is solely for illustrative purposes, and is
not intended to propose a functional code generation keyword.
"allOf": [
"classRelation": "is-a",
"$ref": "classes/base.json"
},
"$ref": "fields/common.json"
],
"properties": {
"foo": {
"classRelation": "has-a",
"$ref": "classes/foo.json"
},
"date": {
"$ref": "types/dateStruct.json",
Here, this schema represents some sort of object-oriented class.
The first reference in the "allOf" is noted as the base class.
The second is not assigned a class relationship, meaning that the
code generator should combine the target's definition with this
one as if no reference were involved.
Looking at the properties, "foo" is flagged as object composition,
while the "date" property is not. It is simply a field with
sub-fields, rather than an instance of a distinct class.
This style of usage requires the annotation to be in the same object
as the reference, which must be recognizable as a reference.
Appendix F.
Acknowledgments
Thanks to
Gary Court,
Francis Galiegue,
Kris Zyp,
and Geraint Luff
for their work on the initial drafts of JSON Schema.
Thanks to
Jason Desrosiers,
Daniel Perrett,
Erik Wilde,
Evgeny Poberezkin,
Brad Bowman,
Gowry Sankar,
Donald Pipowitch,
Dave Finlay,
Denis Laxalde,
Phil Sturgeon,
Shawn Silverman,
and Karen Etheridge
for their submissions and patches to the document.
Appendix G.
ChangeLog
This section to be removed before leaving Internet-Draft status.
draft-bhutton-json-schema-01
Improve and clarify the "type", "contains", "unevaluatedProperties", and "unevaluatedItems" keyword explanations
Clarify various aspects of "canonical URIs"
Comment on ambiguity around annotations and "additionalProperties"
Clarify Vocabularies need not be formally defined
Remove references to remaining media-type parameters
Fix multiple examples
draft-bhutton-json-schema-00
"$schema" MAY change for embedded resources
Array-value "items" functionality is now "prefixItems"
"items" subsumes the old function of "additionalItems"
"contains" annotation behavior, and "contains" and "unevaluatedItems" interactions now specified
Rename $recursive* to $dynamic*, with behavior modification
$dynamicAnchor defines a fragment like $anchor
$dynamic* (previously $recursive) no longer use runtime base URI determination
Define Compound Schema Documents (bundle) and processing
Reference ECMA-262, 11th edition for regular expression support
Regular expression should support unicode
Remove media type parameters
Specify Unknown keywords are collected as annotations
Moved "unevaluatedItems" and "unevaluatedProperties" from core into their own vocabulary
draft-handrews-json-schema-02
Update to RFC 8259 for JSON specification
Moved "definitions" from the Validation specification here as "$defs"
Moved applicator keywords from the Validation specification as their own vocabulary
Moved the schema form of "dependencies" from the Validation specification as "dependentSchemas"
Formalized annotation collection
Specified recommended output formats
Defined keyword interactions in terms of annotation and assertion results
Added "unevaluatedProperties" and "unevaluatedItems"
Define "$ref" behavior in terms of the assertion, applicator, and annotation model
Allow keywords adjacent to "$ref"
Note undefined behavior for "$ref" targets involving unknown keywords
Add recursive referencing, primarily for meta-schema extension
Add the concept of formal vocabularies, and how they can be recognized through meta-schemas
Additional guidance on initial base URIs beyond network retrieval
Allow "schema" media type parameter for "application/schema+json"
Better explanation of media type parameters and the HTTP Accept header
Use "$id" to establish canonical and base absolute-URIs only, no fragments
Replace plain-name-fragment-only form of "$id" with "$anchor"
Clarified that the behavior of JSON Pointers across "$id" boundary is unreliable
draft-handrews-json-schema-01
This draft is purely a clarification with no functional changes
Emphasized annotations as a primary usage of JSON Schema
Clarified $id by use cases
Exhaustive schema identification examples
Replaced "external referencing" with how and when an implementation might know of a schema from another document
Replaced "internal referencing" with how an implementation should recognized schema identifiers during parsing
Dereferencing the former "internal" or "external" references is always the same process
Minor formatting improvements
draft-handrews-json-schema-00
Make the concept of a schema keyword vocabulary more clear
Note that the concept of "integer" is from a vocabulary, not the data model
Classify keywords as assertions or annotations and describe their general behavior
Explain the boolean schemas in terms of generalized assertions
Reserve "$comment" for non-user-visible notes about the schema
Wording improvements around "$id" and fragments
Note the challenges of extending meta-schemas with recursive references
Add "application/schema-instance+json" media type
Recommend a "schema" link relation / parameter instead of "profile"
draft-wright-json-schema-01
Updated intro
Allowed for any schema to be a boolean
"$schema" SHOULD NOT appear in subschemas, although that may change
Changed "id" to "$id"; all core keywords prefixed with "$"
Clarify and formalize fragments for application/schema+json
Note applicability to formats such as CBOR that can be represented in the JSON data model
draft-wright-json-schema-00
Updated references to JSON
Updated references to HTTP
Updated references to JSON Pointer
Behavior for "id" is now specified in terms of RFC3986
Aligned vocabulary usage for URIs with RFC3986
Removed reference to draft-pbryan-zyp-json-ref-03
Limited use of "$ref" to wherever a schema is expected
Added definition of the "JSON Schema data model"
Added additional security considerations
Defined use of subschema identifiers for "id"
Rewrote section on usage with HTTP
Rewrote section on usage with rel="describedBy" and rel="profile"
Fixed numerous invalid examples
draft-zyp-json-schema-04
Salvaged from draft v3.
Split validation keywords into separate document.
Split hypermedia keywords into separate document.
Initial post-split draft.
Mandate the use of JSON Reference, JSON Pointer.
Define the role of "id". Define URI resolution scope.
Add interoperability considerations.
draft-zyp-json-schema-00
Initial draft.
Authors' Addresses
Austin Wright (
editor
Email:
aaa@bzfx.net
Henry Andrews (
editor
Email:
andrews_henry@yahoo.com
Ben Hutton (
editor
Postman
Email:
ben@jsonschema.dev
URI:
Greg Dennis
Email:
gregsdennis@yahoo.com
URI:
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draft-bhutton-json-schema-01
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Authors
Austin Wright
Henry Andrews
Ben Hutton
Greg Dennis
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draft-handrews-json-schema
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