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.
The issues list for this draft can be found at https://github.com/json-schema-org/json-schema-spec/issues.
For additional information, see https://json-schema.org/.
To provide feedback, use this issue tracker, the communication methods listed on the homepage, or email the document editors.
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, and defining terms.
Other specifications define keywords that perform assertions about validation, linking, annotation, navigation, interaction, as well as other related concepts such as output formats.
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.
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.
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 are not supported.
This document defines a set of core keywords that MUST be supported by any
implementation, and cannot be disabled. These keywords are each prefixed with a
"$" character to emphasize their required nature. These keywords are essential
to the functioning of the application/schema+json media type.
Additionally, this document defines a RECOMMENDED set of keywords for applying subschemas conditionally, and for applying subschemas to the contents of objects and arrays. These keywords, or a set very much like them, are 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 set, for maximum interoperability this additional set is included in this document and its use is strongly encouraged.
Further keywords 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 keywords needed to write schemas for that document's purpose.
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 in {{data-model}}.
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.
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 IRI.
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. Extensions to JSON Schema 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 extensions 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 to define as a value for a keyword, but the data model makes no distinction between integers and other numbers.
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.
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.
An extension 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.
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.
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 IRI for the schema and/or changing how the base IRI 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 MUST NOT contain properties which are not schema keywords or are not recognized as schema keywords. The behavior of such keywords is governed by {{unrecognized}}.
An empty schema is a JSON Schema with no properties.
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 defined later 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.
A schema that itself describes a schema is called a meta-schema. Meta-schemas are used to validate JSON Schemas and specify the set of keywords those schemas are using.
A JSON Schema resource is a schema which is canonically identified by an absolute IRI. Schema resources MAY also be identified by IRIs, including IRIs with fragments, if the resulting secondary resource (as defined by section 3.5 of RFC 3986) is identical to the primary resource. This can occur with the empty fragment, or when one schema resource is embedded in another. Any such IRIs 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 IRI is determined as described in {{initial-base}}.1
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 {{id-keyword}}, 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.
In accordance with
section 3.1 of RFC 6839,
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 IRI fragment identifiers is described in RFC
6901. 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,
plain name fragment identifiers in application/schema+json are reserved for
referencing locally named schemas.
Plain name fragments MUST follow XML's
NCName production,
which allows for compatibility with the recommended plain name
syntax for XML-based
media types. For convenience, the NCName syntax is reproduced here in ABNF
form, using a minimal set of rules:
NCName = NCNameStartChar *NCNameChar
NCNameStartChar = "_" / ALPHA
/ %xC0-D6 / %xD8-F6 / %xF8-2FF
/ %x370-37D / %x37F-1FFF
/ %x200C-200D / %x2070-218F
/ %x2C00-2FEF / %x3001-D7FF
/ %xF900-FDCF / %xFDF0-FFFD
/ %x10000-EFFFF
NCNameChar = NCNameStartChar / "-" / "." / DIGIT
/ %xB7 / %x0300-036F / %x203F-2040All fragment identifiers that do not match the JSON Pointer syntax MUST be interpreted as plain name fragment identifiers.
Defining a plain name fragment identifier within an application/schema+json
document is specified in the $anchor keyword section.
An instance may be any valid JSON value as defined by JSON. JSON Schema imposes no restrictions on type: JSON Schema can describe any JSON value, including, for example, null.
JSON Schema is programming language agnostic, and supports the full range of values described in the data model. Be aware, however, that some languages and JSON parsers may not be able to represent in memory the full range of values describable by JSON.
Keywords MAY use regular expressions to express constraints, or constrain the instance value to be a regular expression. These regular expressions SHOULD be valid according to the regular expression dialect described in ECMA-262, section 21.2.1.
Unless otherwise specified by a keyword, regular expressions MUST NOT be considered to be implicitly anchored at either end. All regular expression keywords in this specification and its companion documents are un-anchored.
Regular expressions SHOULD be built with the "u" flag (or equivalent) to provide Unicode support, or processed in such a way which provides Unicode support as defined by ECMA-262.
Furthermore, given the high disparity in regular expression constructs support, schema authors SHOULD limit themselves to the following regular expression tokens:
- individual Unicode characters, as defined by the JSON specification;
- simple atoms:
.(any character except line terminator); - simple character classes (
[abc]), range character classes ([a-z]); - complemented simple character classes (
[^abc]); - complemented range character classes (
[^a-z]); - simple quantifiers:
+(one or more),*(zero or more),?(zero or one), and their non-greedy versions (+?,*?,??); - range quantifiers:
{x}(exactly x occurrences),{x,y}(at least x, at most y, occurrences),{x,}(x occurrences or more), and their non-greedy versions; - the beginning-of-input (
^) and end-of-input ($) anchors; - simple grouping (using
(and)) 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".
Additional schema keywords MAY be defined by any entity. Save for explicit agreement, schema authors SHALL NOT expect these additional keywords to be supported by implementations that do not explicitly document such support.
Implementations MAY provide the ability to register or load handlers for keywords that they do not support directly. The exact mechanism for registering and implementing such handlers is implementation-dependent.
Keywords which begin with "x-" are implicitly defined as annotation keywords.
The values of such keywords MUST be collected as annotations.
Implicit annotation keywords MUST NOT affect evaluation of a schema in any way other than annotation collection.
Consequently, the "x-" prefix is reserved for this purpose, and extension keywords MUST NOT begin with this prefix.
Implementations MUST refuse to evaluate schemas which contain keywords which they do not know how to process or explicitly choose not to process.
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. The interactions of those keyword results to produce the schema object results are governed by {{annot-assert}}, while the relationship of subschema results to the results of the applicator keyword that applied them is described by {{applicators}}.
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.
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 IRI reference, which
must be resolved against another value, such as another IRI reference or a full
IRI, 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 "evaluation 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 evaluation path that produced the error or annotation.
Unless otherwise specified, keywords act independently.
Keywords MAY modify their behavior based on the presence, absence, or value of another keyword in the same schema object. Such keywords MUST NOT result in a circular dependency.
Supplementary specifications are encouraged to specify any dependencies as part of the dependent keyword (i.e. the keyword whose behavior is modified).
Within this document, keyword dependencies are expressed using one of the following mechanisms:
- Static dependencies, in which the dependency relies on the presence or contents of another keyword.
- Dynamic dependencies, in which the dependency relies on the evaluation of another keyword against an instance. This dependency may be on either the annotations produced by the keyword or the validation result of its subschema(s).
These mechanisms are used merely to describe dependencies; they are for illustrative purposes and not prescriptive. Implementations MAY use whatever mechanisms make sense given the needs of their architecture and language in order to achieve the specified 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.
Identifiers define IRIs for a schema, or affect how such IRIs are resolved in
references, or both. This document defines several identifying
keywords, most notably $id.
Canonical schema IRIs MUST NOT change while processing an instance, but keywords that affect IRI reference resolution MAY have behavior that is only fully determined at runtime.
While custom identifier keywords are possible, extension designers should take
care not to disrupt the functioning of core keywords. For example, the
$dynamicAnchor keyword in this specification limits its resolution behavior
to matching $dynamicRef keywords, leaving the behavior of $ref
undisturbed.
Applicators allow for building more complex schemas than can be accomplished with a single schema object. Evaluation of an instance against a schema document begins by applying the root schema 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 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 results from subschemas are preserved in accordance with {{collect}} so that applications can decide how to interpret multiple values. Applicator keywords do not play a direct role in this preservation.
As noted in {{applicators}}, 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, 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.
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.
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 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 specification 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.
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, a keyword's annotation value is value of the
keyword itself. However, other behaviors are possible. For example, JSON
Hyper-Schema's
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.
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 evaluation path, indicating how reference keywords such as
$refwere followed to reach the absolute schema location. - The absolute schema location of the attaching keyword, as a IRI. This MAY be omitted if it is the same as the evaluation path from above.
- The attached value(s)
Applications MAY make decisions on which of multiple annotation values to use based on the schema location that contributed the value. This is intended to allow flexible usage. Collecting the schema location facilitates such usage.
For example, consider this schema, which uses annotations and assertions from the Validation specification:
Note that some lines are wrapped for clarity.
{
"title": "Feature list",
"type": "array",
"prefixItems": [
{
"title": "Feature A",
"properties": {
"enabled": {
"$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 evaluation 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 evaluation 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.
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.
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 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 {{non-schemas}} unrecognized extension keywords that reserve locations for re-usable schemas may have undesirable interactions with references in certain circumstances.
While none of the keywords defined as part of this or the associated documents define a keyword which target and/or load instance data, it is possible that extensions 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.
Keywords declared in this section, which all begin with "$", are essential to processing JSON Schema. These keywords inform implementations how to process any schema or meta-schema, including those split across multiple documents, or exist to reserve keywords for purposes that require guaranteed interoperability.
Support for these keywords MUST be considered mandatory at all times as they are necessary to navigate and process any schema.
The "$" prefix is reserved for use by this specification. Extensions MUST NOT define new keywords that begin with "$".
Meta-schemas are used to inform an implementation how to interpret a schema.
Every schema has a meta-schema, which can be explicitly declared using the
$schema keyword.
The meta-schema serves to describe valid schema syntax. A schema resource MUST successfully validate against its meta-schema, which constrains the syntax of the available keywords. (See {{compound-validation}} for information on validating schemas which contain embedded schema resources that declare a different meta-schema.) The syntax described for a given keyword is expected to be compatible with the document which defines the keyword; while it is possible to describe an incompatible syntax, such a meta-schema would be unlikely to be useful.
Meta-schema authoring is an advanced usage of JSON Schema, so the design of meta-schema features emphasizes flexibility over simplicity.
When evaluation encounters a new schema resource (i.e. the lexical scope changes), the first task is to determine the dialect used by the schema. Implementations MUST determine the dialect using the following prioritized steps.
- The
$schemakeyword - Implementations MUST process the schema according to the dialect it declares. application/schema+jsonmedia type with aschemaparameter - Implementations which support media type parameter inputs MUST process the schema according to the dialect the parameter declares. A media type will generally only be available if the schema has been retrieved from an external source and only applies to the document root.- Parent dialect - An embedded schema resource which does not itself contain a
$schemakeyword MUST be processed using the same dialect as the schema which contains it. If the schema is embedded in a non-schema document, the semantics for determining the dialect MAY be determined by any specification which applies to that document. - User configuration - Implementations MAY provide means for the user to configure the dialect under which a schema should be processed.
(Note that steps 2 and 3 are mutually exclusive.)
If the dialect is not specified through one of these methods, the implementation MUST refuse to process the schema.
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 identified dialect
applies to the resource in which it is declared as well as any embedded schema
resources, unless such a resource itself declares a different dialect by
including the $schema keyword with a different value.
The value of this keyword MUST be an IRI (containing a scheme) and this IRI MUST be normalized.
If this IRI 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. When the
keyword appears in a non-resource root schema object, the behavior is undefined.
Values for this property are defined elsewhere in this and other documents, and by other parties.
To differentiate between schemas in a vast ecosystem, schema resources are identified by absolute IRIs (without fragments). These identifiers are used to create references between schema resources. When comparing IRIs for the purposes of resource identification, implementations SHOULD first follow the IRI normalization procedures defined in RFC 3987, section 5.3.
Several keywords can accept a relative IRI reference, or a value used to construct a relative IRI reference. For these keywords, it is necessary to establish a base IRI in order to resolve the reference.
An $id keyword in a schema or subschema identifies that schema or subschema as
a distinct schema resource. The value for this keyword MUST be a string, and
MUST represent a valid IRI reference without a fragment.
When the value of this keyword is resolved against the current base IRI, the resulting absolute IRI then serves as the identifier for the schema resource and as a base IRI for relative IRI references in keywords within that schema resource and for embedded schema resources, in accordance with RFC 3987 section 6.5 and RFC 3986 section 5.1.1 regarding base IRIs embedded in content and RFC 3986 section 5.1.2 regarding encapsulating entities.
Note that this IRI 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 IRI.
Also note that an $id consisting of an empty IRI only will result in the
embedded resource having the same IRI as the encapsulating resource, which
SHOULD be considered an error per {{duplicate-iris}}.
If no parent schema object explicitly identifies itself as a resource with
$id, the base IRI is that of the entire document, as established by the steps
given in {{initial-base}}.
The root schema of a JSON Schema document SHOULD contain an $id keyword with
an absolute IRI
(containing a scheme, but no fragment).
Using JSON Pointers in IRI fragments to reference subschemas couples the IRI to the structure of the schema. Using plain name fragment identifiers in IRI fragments to identify subschemas is sometimes preferable because it is not tied to a particular structural location. This allows a subschema to be relocated without requiring references to be updated.
The $anchor and $dynamicAnchor keywords are used to define
location-independent identifiers for subschemas within a schema resource.
$anchor defines a plain name fragment identifier that can be used in IRI
fragments as an alternative to JSON Pointers.2 See {{fragments}}.
$dynamicAnchor defines a different kind of fragment identifier that only has
meaning when used with $dynamicRef. It's not a normal fragment identifier and
therefore can't be used anywhere other than $dynamicRef. Normal fragment
identifiers identify the
secondary resource (the subschema) while the rest of the IRI identifies the
primary resource (the schema resource). The fragment identifiers defined by
$dynamicAnchor are not normal fragment identifies because they identify both
the primary resource and the secondary resource. See {{dynamic-ref}} for
details.
If present, the value of these keywords MUST be a string and MUST conform to the plain name fragment identifier syntax defined in {{fragments}}.
A schema MAY (and likely will) have multiple IRIs, but there is no way for an
IRI to identify more than one schema. When multiple schemas attempt to identify
as the same IRI through the use of $id, $anchor, $dynamicAnchor, or any
other mechanism, implementations SHOULD raise an error condition. Otherwise the
result is undefined, and even if documented will not be interoperable.
$ref and $dynamicRef can be used to reference a schema which is to be
applied to the current instance location. As such, they are considered
applicators, applying the referenced schema to the instance.
The $ref keyword is an applicator that is used to reference a statically
identified schema. Its results are the results of the referenced schema.3
The value of the $ref keyword MUST be a string which is an IRI reference.
Resolved against the current IRI base, it produces the IRI 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.
The resolved IRI produced by $ref 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. Implementations which can access the network SHOULD
default to operating offline.
The $dynamicRef keyword is an applicator that is used when the referencing
schema might need to override where a reference in the referenced schema will
resolve. This is useful for cases such as authoring a recursive schema that can
be extended or a generic schema such as a list whose items are defined by the
referencing schema.
The value of the $dynamicRef property MUST be formatted as a valid
fragment-only IRI.4
Resolution of $dynamicRef begins by identifying the outermost schema resource
in the dynamic scope which defines a matching $dynamicAnchor. The
schema to apply is the subschema of this resource which contains the matching
$dynamicAnchor. If no matching $dynamicAnchor is found, see {{failed-refs}}.
For a full example using these keywords, see {{dynamic-example}}.5
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
}
}
}
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.
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.
RFC 3987 Section 6.5 and RFC 3986 Section 5.1 defines how to determine the default base IRI of a document.
Informatively, the initial base IRI of a schema is the IRI at which it was found, whether that was a network location, a local filesystem, or any other situation identifiable by a IRI of any known scheme.
If a schema document defines no explicit base IRI with $id (embedded in
content), the base IRI is that determined per RFC 3987 Section 6.5
and RFC 3986 section 5.
If no source is known, or no IRI scheme is known for the source, a suitable implementation-specific default IRI MAY be used as described in RFC 3987 Section 6.5 and RFC 3986 Section 5.1.4. It is RECOMMENDED that implementations document any default base IRI that they assume.
If a schema object is embedded in a document of another media type, then the initial base IRI 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 IRI SHOULD be considered the canonical IRI of the schema
document's root schema resource.
The use of IRIs 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 IRIs that identify them.
Implementations SHOULD be able to associate arbitrary IRIs with an arbitrary
schema and/or automatically associate a schema's $id-given IRI, depending on
the trust that the validator has in the schema. Such IRIs 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
{{idexamples}}.
Implementations MAY provide functionality to automatically fetch schemas based on location semantics expressed by the IRI, however such functionality SHOULD be disabled by default to prefer offline operation. When schemas are downloaded, for example by a generic user-agent that does not know until runtime which schemas to download, see {{hypermedia}}.
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 requirements up front. Meta-schema authors MUST NOT expect such features to be interoperable across implementations.
Schemas can be identified by any IRI that has been given to them, including a
JSON Pointer or their IRI given directly by $id. In all cases, dereferencing a
$ref reference involves first resolving its value as a IRI reference against
the current base IRI per RFC 3986.
If the resulting IRI identifies a schema within the current document, or within another schema document that has been made available to the implementation, then that schema SHOULD be used automatically.
For example, consider this schema:
{
"$id": "https://example.net/root.json",
"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
$anchor value as a fragment name against the current base IRI to form
https://example.net/root.json#item.
When an implementation then looks inside the #/items schema, it encounters the
#item reference, and resolves this to https://example.net/root.json#item,
which it has seen defined in this same document and can therefore use
automatically.
When an implementation encounters the reference to "other.json", it resolves
this to https://example.net/other.json, which is not defined in this document.
If an implementation has been configured to resolve that identifier to a schema
via pre-loading or other means, it can be used automatically; otherwise, the
behavior described in {{failed-refs}} MUST be used.
Since JSON Pointer fragment identifiers are based on the structure of the schema document, an embedded schema resource and its subschemas can be identified using JSON Pointer IRI fragments relative to either its own IRI, or relative to any containing resource's IRI.
Conceptually, a set of linked schema resources should behave identically whether each resource is a separate document connected with schema references, or is structured as a single document with one or more schema resources embedded as subschemas.
Since IRIs with JSON Pointer fragments are relative to the parent schema resource's IRI, they cease to be valid when the embedded schema is moved to a separate document and referenced. Because of this, applications and schemas SHOULD NOT use such IRIs to identify embedded schema resources or locations within them.
Consider the following schema document that contains another schema resource embedded within it:
{
"$id": "https://example.com/foo",
"items": {
"$id": "https://example.com/bar",
"additionalProperties": { }
}
}
The IRI https://example.com/foo#/items points to the items schema, which is
an embedded resource. The canonical IRI of that schema resource, however, is
https://example.com/bar.
For the additionalProperties schema within that embedded resource, the IRI
https://example.com/foo#/items/additionalProperties points to the correct
object, but that object's IRI relative to its resource's canonical IRI is
https://example.com/bar#/additionalProperties.
Now consider the following two schema resources linked by reference using an IRI
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 identifier appended to the canonical IRI of the "bar" schema
resource, is still valid, while
https://example.com/foo#/items/additionalProperties, which relied on a JSON
Pointer fragment identifier appended to the canonical IRI 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 IRI ends up functioning similarly to a
retrieval IRI for a resource. While this IRI 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.
Due to the potential break in functionality described above, the behavior for using JSON Pointer fragments that point to or cross a resource boundary is undefined. Schema authors SHOULD NOT rely on such IRIs, as using them may reduce interoperability.6
Further examples of such non-canonical IRI construction, as well as the appropriate canonical IRI-based fragments to use instead, are provided in {{idexamples}}.
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 keyword support.
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 IRIs (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 IRI 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 IRI identifier value of $id be an Absolute IRI.
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 identifier (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 IRIs 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.
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.
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.7
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.
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.
Subschema objects (or booleans) are recognized by their use with known
applicator keywords or with location-reserving keywords, such as
$defs, that take one or more subschemas as a value. These keywords
include the standard applicators from this document or implementation-specific
custom keywords.
A reference target under a keyword for which the value is not explicitly known to be a schema results in undefined behavior. Implementations MAY support references to these locations, however such behavior is not considered interoperable and should not be relied upon.8
If for any reason a reference cannot be resolved, the evaluation MUST halt and return an indeterminant result. Specifically, it MUST NOT return a passing or failing validation result or any annotations. Instead it MUST inform the consuming application or user of the evaluation failure via other means. It is RECOMMENDED that implementations utilize native functionality for this purpose, such as, but not limited to, raising an exception or other error.
In the cases where optimizations are enabled and a schema containing a non-resolvable reference would be skipped, as in the example below, behavior is implementation-defined.
{
"anyOf": [
true,
{ "$ref": "https://json-schema.org/does-not-exist" }
]
}Here, an optimized evaluation may recognize that /anyOf/0 will satisfy the
anyOf constraint, regardless of the validation result of /anyOf/1, and so
/anyOf/1 may be skipped altogether.
However, an unoptimized evaluation of this schema (for example one that expects all annotation results), would result in a resolution failure.
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.
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.
In HTTP, such links can be attached to any response using the Link header. An example of such a header would be:
Link: <https://example.com/my-hyper-schema>; rel="describedby"
When used for hypermedia systems over a network, HTTP 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.
This section defines a set of keywords that enable schema combinations and composition.
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.
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.
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.
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.
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.
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.
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.
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 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.
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 the if subschema. Implementations MUST NOT evaluate the
instance against this keyword, for either validation or annotation collection
purposes, in such cases.
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 the if subschema. Implementations MUST NOT
evaluate the instance against this keyword, for either validation or annotation
collection purposes, in such cases.
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.
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.
When working with arrays and indices, JSON Schema uses zero-based indexing. This aligns with both JSON's JavaScript heritage and its usage of JSON Pointer for references and annotations.
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 subschema at the same position, if any. This keyword does not constrain the length of the array. Only array positions present in both the keyword's value and the instance value are affected by this keyword.
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.
The presence of this keyword affects the behaviors of items and
unevaluatedItems.
The value of items MUST be a valid JSON Schema.
This keyword ignores elements in the instance array equal to the number of
subschemas found in the prefixItems array in the same schema object, starting
from the beginning of the instance array. It then applies its subschema to
remaining elements.
If prefixItems contains more subschemas than the number of elements in the
instance array, items applies its subschema to no elements.
If prefixItems does not exist within the same schema object, items applies
its subschema to all elements.
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.
Omitting this keyword has the same assertion behavior as an empty schema.
The presence of this keyword affects the behavior of
unevaluatedItems.
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.
Omitting this keyword has the same assertion behavior as an empty object.
The annotation result of this keyword is the set of instance property names which are also present under this keyword.
The presence of this keyword affects the behaviors of
[additionalProperties(#additionalProperties) and unevaluatedProperties.
The value of patternProperties MUST be an object. Each property name of this
object SHOULD be a valid regular expression as indicated in {{regex}}. 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. Recall: regular expressions are not implicitly anchored.
Omitting this keyword has the same assertion behavior as an empty object.
The annotation result of this keyword is the set of instance property names matched by at least one property under this keyword.
The presence of this keyword affects the behaviors of
[additionalProperties(#additionalproperties) and
unevaluatedProperties.
The value of additionalProperties MUST be a valid JSON Schema.
The behavior of this keyword depends on the presence of properties and
patternProperties within the same schema object. Validation with
additionalProperties applies only to the property values for which neither
properties nor patternProperties apply.
For all such properties, validation succeeds if the child instance validates
against the additionalProperties schema.
Omitting this keyword has the same assertion behavior as an empty schema.
The annotation result of this keyword is the set of instance property names validated by this keyword's subschema.
The presence of this keyword affects the behavior of
unevaluatedProperties.
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.
The value of this keyword MUST be a non-negative integer.
This keyword modifies the behavior of contains within the same schema object,
as described below in the section for that keyword.
Validation MUST always succeed against this keyword. The value of this keyword is used as its annotation result.
The value of this keyword MUST be a non-negative integer.
This keyword modifies the behavior of contains within the same schema object,
as described below in the section for that keyword.
Validation MUST always succeed against this keyword. The value of this keyword is used as its annotation result.
Per {{default-behaviors}}, omitted keywords MUST NOT produce annotation results.
However, as described in {{contains}}, the absence of this keyword's annotation
causes contains to assume a minimum value of 1.
The value of this keyword MUST be a valid JSON Schema.
This keyword applies to array instances by applying its subschema to the array's elements.
An instance is valid against contains if the number of elements that are valid
against its subschema is within the inclusive range of the minimum and (if any)
maximum number of occurrences.
The maximum number of occurrences is provided by the maxContains keyword
within the same schema object as contains. If maxContains is absent, the
maximum number of occurrences MUST be unbounded.
The minimum number of occurrences is provided by the minContains keyword
within the same schema object as contains. If minContains is absent, the
minimum number of occurrences MUST be 1.
This keyword produces an annotation value which is an array of the zero-based
indices for 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.
The presence of this keyword affects the behavior of
unevaluatedItems.
Under most circumstances, the contains subschema MAY be short-circuited.
However, for the following cases, the contains subschema MUST be applied to
every array element.
- If
unevaluatedItemsappears in any subschema in the dynamic scope that applies to the same instance location, to ensure that all evaluated items are accounted for. - When collecting annotations, to ensure that all annotations are found.
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 thus the "wheels" property is considered "unevaluated".
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 behaviors of these keywords depend on adjacent keywords as well as any keywords in successfully validated subschemas that apply to the same instance location.
The value of unevaluatedItems MUST be a valid JSON Schema.
This keyword applies to array instances by applying its subschema to the array's elements.
The behavior of this keyword depends on all adjacent keywords as well as
keywords in successfully validated subschemas that apply to the same instance
location by evaluating the instance's elements. This includes, but is not
limited to, prefixItems, items, and contains, itself, and all
in-place applicators defined in this document.
This keyword applies its subschema to any array elements which have not been deemed "evaluated" per {{unevaluated}}. Validation passes if the keyword's subschema validates against all applicable array elements.
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.
The presence of this keyword affects the behavior of other unevaluatedItems
keywords found earlier in the dynamic scope that apply to the same instance
location.
Omitting this keyword has the same assertion behavior as an empty schema.
The value of unevaluatedProperties MUST be a valid JSON Schema.
This keyword applies to object instances by applying its subschema to the object's property values.
The behavior of this keyword depends on all adjacent keywords as well as
keywords in successfully validated subschemas that apply to the same instance
location by evaluating the instance's property values. This includes, but is not
limited to, properties, patternProperties, and additionalProperties,
itself, and all in-place applicators defined in this document.
This keyword applies its subschema to any property values which have not been deemed "evaluated" per {{unevaluated}}. Validation passes if the keyword's subschema validates against all applicable property values.
The annotation result of this keyword is the set of instance property names validated by this keyword's subschema.
The presence of this keyword affects the behavior of other
unevaluatedProperties keywords found earlier in the dynamic scope that apply
to the same instance location.
Omitting this keyword has the same assertion behavior as an empty schema.
In order to foster increased usability and interoperability, implementations SHOULD adhere to well-defined output formats.
Because JSON Schema has multiple uses cases, and those uses cases have different intended consumers, this specification defers the details of any output formats to other documents. Implementations are encouraged to support multiple output formats as required by their target user base.
The scope of this section, therefore, is limited to defining common terms that SHOULD be used in JSON Schema output specifications in order to align the vernacular across differing formats. Output specifications which use this information MUST use this terminology to describe it. Conversely, output specifications which use these terms MUST maintain their meaning.
The evaluation path is the set of keys, starting from the schema root, through
which evaluation passes to reach the schema object that produced a specific
result. 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/allOf/1
Note that this pointer may not be resolvable on the root schema by the normal JSON Pointer process. It is intended as an indication of the traversal path only.
When represented in JSON, the key for this information MUST be "evaluationPath".
The schema location is the canonical URI of the schema object plus a JSON
Pointer fragment indicating the subschema that produced a result. In contrast
with the evaluation path, the schema location MUST NOT include by-reference
applicators such as $ref or $dynamicRef.
https://example.com/schemas/common#/$defs/allOf/1
The instance location is the location of the JSON value within the root instance being validated. The value MUST be expressed as a JSON Pointer.
Errors are textual representations of individual validation failures, often intended for human consumers. This specification contains no requirements for the content of these errors.
Output specifications which include errors SHOULD be written such that the sources (schema and instance) of a given error is easily identifiable and SHOULD use the terms defined by this document to do so.
Many keywords are defined to produce annotations, whether intended for
inter-keyword communication (e.g. between properties and
unevaluatedProperties) or for application consumption (e.g. title or
readOnly). Annotation values may be of any type and are defined by the
keywords that produced them.
Output specifications which include annotations SHOULD be written such that they can be easily associated with the data defined in {{collect}} and SHOULD use the terms defined by this document to do so.
A dropped annotation is any annotation produced and subsequently dropped by the evaluation due to an unsuccessful validation result of the containing subschema. This information MAY be included if the validation result of the containing subschema was unsuccessful. It MUST NOT be included if the local validation result of the containing subschema was successful.
As the intended purpose for including these annotations is debugging, implementations that wish to provide dropped annotations SHOULD NOT provide them as their default behavior. Dropped annotations SHOULD only be included when the implementation is explicitly configured to do so or if the implementation is specifically intended to be used as a debugging tool.
Output specifications which include dropped annotations SHOULD be written such that they can be easily associated with the data defined in {{collect}} and SHOULD use the terms defined by this document to do so.
Both schemas and instances are JSON values. As such, all security considerations defined in RFC 8259 apply.
Instances and schemas are both frequently written by untrusted third parties, to be deployed on public Internet servers. Implementations should take care that the parsing and evaluating against schemas does not consume excessive system resources. Implementations 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 extensions 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.
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.
Security considerations:: See {{security}} above.
Interoperability considerations:: See Sections 6.2, 6.3, and 6.4 above.
Fragment identifier considerations:: See {{fragments}}
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.
Security considerations:: See {{security}} above.
Interoperability considerations:: See Sections 6.2, 6.3, and 6.4 above.
Fragment identifier considerations:: See {{fragments}}
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 locations (indicated by plain JSON Pointers relative to the root document) have the following base IRIs, and are identifiable by any listed IRI in accordance with {{fragments}} and {{embedded}} above.
Document root:
- canonical (and base) IRI:
https://example.com/root.json - canonical resource IRI plus pointer fragment:
https://example.com/root.json#
Document location /$defs/A:
- base IRI:
https://example.com/root.json - canonical resource IRI plus plain fragment:
https://example.com/root.json#foo - canonical resource IRI plus pointer fragment:
https://example.com/root.json#/$defs/A
Document location /$defs/B:
- canonical (and base)
IRI: https://example.com/other.json - canonical resource IRI plus pointer fragment:
https://example.com/other.json#
Document location /$defs/B/$defs/X:
- base IRI:
https://example.com/other.json - canonical resource IRI plus plain fragment:
https://example.com/other.json#bar - canonical resource IRI plus pointer fragment:
https://example.com/other.json#/$defs/X
Document location /$defs/B/$defs/Y:
- canonical (and base) IRI:
https://example.com/t/inner.json - canonical IRI plus plain fragment:
https://example.com/t/inner.json#bar - canonical IRI plus pointer fragment:
https://example.com/t/inner.json#
Document location /$defs/C:
- canonical (and base) IRI:
urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f - canonical IRI plus pointer fragment:
urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f#
Note: The fragment part of the IRI does not make it canonical or non-canonical, rather, the base IRI used (as part of the full IRI with any fragment) is what determines the canonical nature of the resulting full IRI.9
While the following IRIs do correctly indicate specific schemas, per the reasons outlined in {{embedded}}, they are to be avoided as they may not work in all implementations:
Document location /$defs/B:
- canonical (and base)
IRI: https://example.com/other.json - base IRI of enclosing (root.json) resource plus fragment:
https://example.com/root.json#/$defs/B
Document location /$defs/B/$defs/X:
- base IRI:
https://example.com/other.json - base IRI of enclosing (root.json) resource plus fragment:
https://example.com/root.json#/$defs/B/$defs/X
Document location /$defs/B/$defs/Y:
- canonical (and base) IRI:
https://example.com/t/inner.json - base IRI of enclosing (other.json) resource plus fragment:
https://example.com/other.json#/$defs/Y - base IRI of enclosing (root.json) resource plus fragment:
https://example.com/root.json#/$defs/B/$defs/Y
Document location /$defs/C:
- canonical (and base) IRI:
urn:uuid:ee564b8a-7a87-4125-8c96-e9f123d6766f - base IRI of enclosing (root.json) resource plus fragment:
https://example.com/root.json#/$defs/C
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.
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 IRI references that resolve to IRIs using the
canonical resource IRI as the base, and all schema resources have an
absolute IRI 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 IRIs for the embedded resources.
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 $ref removal
transformations, as they depend not only on the schema structure but also on the
intended usage.
Consider the following two schemas describing a simple recursive tree structure, where each node in the tree can have a "data" field of any type. The first schema allows and ignores other instance properties. The second is more strict and only allows the "data" and "children" properties. An example instance with "data" misspelled as "daat" is also shown.
{
"$schema": "https://json-schema.org/draft/next/schema",
"$id": "https://example.com/tree",
"$dynamicAnchor": "node",
"type": "object",
"properties": {
"data": true,
"children": {
"type": "array",
"items": {
"$dynamicRef": "#node"
}
}
}
}
{
"$schema": "https://json-schema.org/draft/next/schema",
"$id": "https://example.com/strict-tree",
"$dynamicAnchor": "node",
"$ref": "tree",
"unevaluatedProperties": false
}
{
"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 IRIs:
https://example.com/tree#nodehttps://example.com/strict-tree#node
In addition, JSON Schema implementations keep track of the fact that these
fragment identifiers 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 IRI fragment syntax) in its items
subschema. That reference resolves to https://example.com/tree#node, which is
a IRI with a fragment created by $dynamicAnchor. Therefore we must examine the
dynamic scope before following the reference.
At this point, the evaluation path is
/$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/childrenhttps://example.com/tree#/properties/children/items
Since we are looking for a plain name fragment identifier, which can be defined anywhere within a schema resource, the JSON Pointer IRI fragments are irrelevant to this check. That means that we can remove the fragments and eliminate consecutive duplicates, producing:
https://example.com/strict-treehttps://example.com/tree
In this case, the outermost resource also has a "node" fragment identifier
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.
The reference in the "tree" schema resolves to the root of "strict-tree", so "strict-tree" is applied not only to the tree instance's root, but also its children.
This example shows both $dynamicAnchors in the same place in each schema,
specifically the resource root schema. Since plain-name fragment identifiers 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.
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": {
"$ref": "types/dateStruct.json",
}
}
}
Here, this schema represents some sort of object-oriented class. The first
reference in the allOf is noted as the base class. The second is not assigned
a class relationship, meaning that the code generator should combine the
target's definition with this one as if no reference were involved.
Looking at the properties, "foo" is flagged as object composition, while the "date" property is not. It is simply a field with sub-fields, rather than an instance of a distinct class.
This style of usage requires the annotation to be in the same object as the reference, which must be recognizable as a reference.
Thanks to Gary Court, Francis Galiegue, Kris Zyp, Geraint Luff, and Henry Andrews for their work on the initial drafts of JSON Schema.
Thanks to Jason Desrosiers, Daniel Perrett, Erik Wilde, Evgeny Poberezkin, Brad Bowman, Gowry Sankar, Donald Pipowitch, Dave Finlay, Denis Laxalde, Phil Sturgeon, Shawn Silverman, and Karen Etheridge for their submissions and patches to the document.
%appendix% Change Log10
- Use IRIs instead of URIs, including allowing unicode in plain-name fragments
- Clarify that detecting duplicate IRIs for different schemas SHOULD raise an error
- Consolidate and clarify the syntax and rationale for plain-name fragments
- "$id" MUST be an absolute IRI, without any fragment, even an empty one
- Note that an empty string "$id" results in duplicate IRIs for different schemas
- Define empty schemas as empty (no longer allowing unrecognized keywords)
- Clarify that if unknown properties are not treated as annotations, they MUST be ignored
- Remove outdated pre-annotation-collection section on annotation-applicator interaction
- Clarify that regular expressions are not anchored
- Specify valid implementation-defined options for handling schemas without "$schema"
- Clarify that vocabularies omitted from "$vocabulary" MUST NOT be available for use
- Clarify that standard keywords are only available as vocabulary keywords, subject to "$vocabulary" control
- Clarify the nature and purpose of optional (set to false in "$vocabulary") vocabularies
- Clarify that optional simple-annotation-only vocabularies can be supported without custom code
- Fix typo that "$vocabulary" can only be in a document root; it is legal in resource roots
- Remove bookending requirement for
$dynamicRef - Clarify that "prefixItems" does not constrain the length of an array
- Move "minContains" and "maxContains" to the applicator vocabulary from validation
- "minContains" and "maxContains" no longer have their own assertion results
- "contains" assertion result now depends on "minContains" and "maxContains"
- Affirm that no keyword can un-fail an adjacent keyword ("minContains" previously violated this)
- "contains", "minContains", and "maxContains" now apply to objects as well as arrays
- As an object keyword, "contains" now affects "unevaluatedProperties"
- Add
propertyDependencieskeyword - Add new "list" and "hierarchical" output formats in place of "basic", "detailed", and "verbose"
- Rename "absoluteKeywordLocation" and "keywordLocation" to "schemaLocation" and "evaluationPath"
- Output units in new format group by "schemaLocation", "instanceLocation", and "evaluationPath"
- Add "droppedAnnotations" to output formats
- Improve and clarify the
type,contains,unevaluatedProperties, andunevaluatedItemskeyword 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
$schemaMAY change for embedded resources- Array-value
itemsfunctionality is nowprefixItems itemssubsumes the old function ofadditionalItemscontainsannotation behavior, andcontainsandunevaluatedItemsinteractions now specified- Rename $recursive* to $dynamic*, with behavior modification
- $dynamicAnchor defines a fragment like $anchor
- $dynamic* (previously $recursive) no longer use runtime base URI determination
- Define Compound Schema Documents (bundle) and processing
- Reference ECMA-262, 11th edition for regular expression support
- Regular expression should support unicode
- Remove media type parameters
- Specify Unknown keywords are collected as annotations
- Moved
unevaluatedItemsandunevaluatedPropertiesfrom core into their own vocabulary
- Update to RFC 8259 for JSON specification
- Moved
definitionsfrom the Validation specification here as$defs - Moved applicator keywords from the Validation specification as their own vocabulary
- Moved the schema form of
dependenciesfrom the Validation specification asdependentSchemas - Formalized annotation collection
- Specified recommended output formats
- Defined keyword interactions in terms of annotation and assertion results
- Added
unevaluatedPropertiesandunevaluatedItems - Define
$refbehavior in terms of the assertion, applicator, and annotation model - Allow keywords adjacent to
$ref - Note undefined behavior for
$reftargets 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
$idto establish canonical and base absolute-URIs only, no fragments - Replace plain-name-fragment-only form of
$idwith$anchor - Clarified that the behavior of JSON Pointers across
$idboundary is unreliable
- 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
- 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
$commentfor non-user-visible notes about the schema - Wording improvements around
$idand fragments - Note the challenges of extending meta-schemas with recursive references
- Add
application/schema-instance+jsonmedia type - Recommend a "schema" link relation / parameter instead of "profile"
- Updated intro
- Allowed for any schema to be a boolean
$schemaSHOULD NOT appear in subschemas, although that may change- Changed
idto$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
- Updated references to JSON
- Updated references to HTTP
- Updated references to JSON Pointer
- Behavior for
idis 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
$refto 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
- 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.
- Initial draft.
| Author | Company | URI | |
|---|---|---|---|
| Austin Wright (editor) | aaa@bzfx.net | ||
| Ben Hutton (editor) | Postman | ben@jsonschema.dev | https://jsonschema.dev |
| Greg Dennis | gregsdennis@yahoo.com | https://github.com/gregsdennis |
Footnotes
-
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. ↩
-
Note that the anchor string does not include the "#" character, as it is just a fragment identifier not an IRI reference. To reference the "foo"
$anchorfrom the same schema resource, you would use the fragment-only IRI#foo. See below for full examples. ↩ -
Note that this definition of how the results are determined means that other keywords can appear alongside of
$refin the same schema object. ↩ -
$dynamicAnchordefines the anchor with plain text, e.g.foo. Although, for historical reasons, the value of$dynamicRefstill uses a fragment-only IRI syntax, e.g.#foo. ↩ -
The differences in the hyper-schema meta-schemas from draft-07 and draft 2019-09 dramatically demonstrates the utility of these keywords. ↩
-
This is to avoid requiring implementations to keep track of a whole stack of possible base IRIs and JSON Pointer fragment identifiers 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, https://github.com/json-schema-org/json-schema-spec/issues/1183) ↩
-
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. ↩ -
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 implication and may produce unpredictable results. ↩ -
Multiple "canonical" IRIs? We Acknowledge this is potentially confusing, and direct you to read the CREF located in {{embedded}} for further comments. ↩
-
This section to be removed before leaving Internet-Draft status. ↩