JSON Schema Validation: A Vocabulary for Structural Validation of JSON

Abstract

JSON Schema (application/schema+json) has several purposes, one of which is JSON instance validation. This document specifies a vocabulary for JSON Schema to describe the meaning of JSON documents, provide hints for user interfaces working with JSON data, and to make assertions about what a valid document must look like.

Note to Readers

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.

Introduction

JSON Schema can be used to require that a given JSON document (an instance) satisfies a certain number of criteria. These criteria are asserted by using keywords described in this specification. In addition, a set of keywords is also defined to assist in interactive user interface instance generation.

This specification will use the concepts, syntax, and terminology defined by the JSON Schema core specification.

Conventions and Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

This specification uses the term "container instance" to refer to both array and object instances. It uses the term "children instances" to refer to array elements or object member values.

Elements in an array value are said to be unique if no two elements of this array are equal.

Overview

JSON Schema validation asserts constraints on the structure of instance data. An instance location that satisfies all asserted constraints is then annotated with any keywords that contain non-assertion information, such as descriptive metadata and usage hints. If all locations within the instance satisfy all asserted constraints, then the instance is said to be valid against the schema.

Each schema object is independently evaluated against each instance location to which it applies. This greatly simplifies the implementation requirements for validators by ensuring that they do not need to maintain state across the document-wide validation process.

This specification defines a set of assertion keywords, as well as a number of metadata keywords that can be used to annotate the JSON instance with useful information. The {{format}} keyword is intended primarily as an annotation, but can optionally be used as an assertion. The {{content}} keywords are annotations for working with documents embedded as JSON strings.

Keyword Behaviors

The keywords defined by this document exhibit one or more behaviors as defined by the JSON Schema Core Specification.

Keywords which are not defined to exhibit a particular behavior MUST NOT affect that aspect of the evaluation outcome. In particular, the keywords defined in {{annotations}} produce no assertion result and therefore are not considered during validation.

For the purposes of this document, an instance "validating against a keyword" means that the keyword produces an assertion result of true if the instance satisfies the given constraint; otherwise an assertion result of false is produced.

Interoperability Considerations

Validation of String Instances

It should be noted that the nul character (\u0000) is valid in a JSON string. An instance to validate may contain a string value with this character, regardless of the ability of the underlying programming language to deal with such data.

Validation of Numeric Instances

The JSON specification allows numbers with arbitrary precision, and JSON Schema does not add any such bounds. This means that numeric instances processed by JSON Schema can be arbitrarily large and/or have an arbitrarily long decimal part, regardless of the ability of the underlying programming language to deal with such data.

Regular Expressions {#regexinterop}

Keywords that use regular expressions, or constrain the instance value to be a regular expression, are subject to the interoperability considerations for regular expressions in the JSON Schema Core specification.

Meta-Schema {#meta-schema}

The current IRI for the default JSON Schema dialect meta-schema is https://json-schema.org/v1/2026. This IRI encodes the specification's version and release year. Because all schemas written to conform to a given version are guaranteed to be compatible with later releases within the same version, the meta-schema IRI https://json-schema.org/v1 is also recognized to represent the latest release within the indicated version.

The meta-schema describes a dialect consisting of all keywords defined in this specification and the JSON Schema Core specification. Certain keywords specify some functionality which is optional to support and is explained in detail in the relevant sections.

Where the meta-schema conflicts with either this specification or the JSON Schema Core specification, the specifications take precedence, and the meta-schema is to be considered in error. The meta-schema may be occasionally updated to correct any such errors.

Although the IRI for the default JSON Schema dialect meta-schema is also a valid URL, implementations MUST NOT assume that a document is provided at this location. Rather than performing a network request to retrieve the meta-schema, implementations SHOULD include a copy of the meta-schema and MAY encode it as required by the language or framework used by the implementation.

Keywords for Structural Validation

Validation keywords in a schema impose requirements for successful validation of an instance. These keywords are all assertions without any annotation behavior.

Validation Keywords for Any Instance Type {#general}

`type`

The value of this keyword MUST be either a string or an array. If it is an array, it MUST be non-empty, and elements of the array MUST be strings and MUST be unique.

String values MUST be one of the six primitive types ("null", "boolean", "object", "array", "number", or "string"), or "integer" which matches any number with a zero fractional part.

If the value of type is a string, then an instance validates successfully if its type matches the type represented by the value of the string.

If the value of type is an array, then an instance validates successfully if its type matches any of the types indicated by the strings in the array.

`enum` {#enum}

The value of this keyword MUST be an array. This array SHOULD have at least one element. Elements in the array SHOULD be unique.

An instance validates successfully against this keyword if its value is equal to one of the elements in this keyword's array value.

Elements in the array might be of any type, including null.

`const`

The value of this keyword MAY be of any type, including null.

Use of this keyword is functionally equivalent to an enum with a single value.

An instance validates successfully against this keyword if its value is equal to the value of the keyword.

Validation Keywords for Numeric Instances (number and integer) {#numeric}

`multipleOf`

The value of multipleOf MUST be a number, strictly greater than 0.

A numeric instance is valid only if division by this keyword's value results in an integer.

`maximum`

The value of maximum MUST be a number, representing an inclusive upper limit for a numeric instance.

If the instance is a number, then this keyword validates only if the instance is less than or exactly equal to maximum.

`exclusiveMaximum`

The value of exclusiveMaximum MUST be a number, representing an exclusive upper limit for a numeric instance.

If the instance is a number, then the instance is valid only if it has a value strictly less than (not equal to) exclusiveMaximum.

`minimum`

The value of minimum MUST be a number, representing an inclusive lower limit for a numeric instance.

If the instance is a number, then this keyword validates only if the instance is greater than or exactly equal to minimum.

`exclusiveMinimum`

The value of exclusiveMinimum MUST be a number, representing an exclusive lower limit for a numeric instance.

If the instance is a number, then the instance is valid only if it has a value strictly greater than (not equal to) exclusiveMinimum.

Validation Keywords for Strings {#string}

`maxLength`

The value of this keyword MUST be a non-negative integer.

A string instance is valid against this keyword if its length is less than, or equal to, the value of this keyword.

The length of a string instance is defined as the number of Unicode code points that make up the string.

`minLength`

The value of this keyword MUST be a non-negative integer.

A string instance is valid against this keyword if its length is greater than, or equal to, the value of this keyword.

The length of a string instance is defined as the number of Unicode code points that make up the string.

Omitting this keyword has the same behavior as a value of 0.

`pattern` {#pattern}

The value of this keyword MUST be a string. This string SHOULD be a valid regular expression as indicated in JSON Schema Core, section 6.3.

A string instance is considered valid if the regular expression matches the instance successfully. Recall: regular expressions are not implicitly anchored.

Validation Keywords for Arrays

`maxItems`

The value of this keyword MUST be a non-negative integer.

An array instance is valid against maxItems if its size is less than, or equal to, the value of this keyword.

`minItems`

The value of this keyword MUST be a non-negative integer.

An array instance is valid against minItems if its size is greater than, or equal to, the value of this keyword.

Omitting this keyword has the same behavior as a value of 0.

`uniqueItems`

The value of this keyword MUST be a boolean.

If this keyword has boolean value false, the instance validates successfully. If it has boolean value true, the instance validates successfully if all of its elements are unique.

Omitting this keyword has the same behavior as a value of false.

Validation Keywords for Objects

`maxProperties`

The value of this keyword MUST be a non-negative integer.

An object instance is valid against maxProperties if its number of properties is less than, or equal to, the value of this keyword.

`minProperties`

The value of this keyword MUST be a non-negative integer.

An object instance is valid against minProperties if its number of properties is greater than, or equal to, the value of this keyword.

Omitting this keyword has the same behavior as a value of 0.

`required`

The value of this keyword MUST be an array. Elements of this array, if any, MUST be strings, and MUST be unique.

An object instance is valid against this keyword if every item in the array is the name of a property in the instance.

Omitting this keyword has the same behavior as an empty array.

`dependentRequired`

The value of this keyword MUST be an object. Properties in this object, if any, MUST be arrays. Elements in each array, if any, MUST be strings, and MUST be unique.

This keyword specifies properties that are required if a specific other property is present. Their requirement is dependent on the presence of the other property.

Validation succeeds if, for each name that appears in both the instance and as a name within this keyword's value, every item in the corresponding array is also the name of a property in the instance.

Omitting this keyword has the same behavior as an empty object.

Semantic Content With `format` {#format}

Foreword

Structural validation alone may be insufficient to allow an application to correctly utilize certain values. The format annotation keyword is defined to allow schema authors to convey semantic information for a fixed subset of values which are accurately described by authoritative resources, be they RFCs or other external specifications. Format values defined externally to this document SHOULD also be based on such authoritative resources in order to foster interoperability.

The value of this keyword MUST be a string. While this keyword can validate any type, each distinct value will generally only validate a given set of instance types. If the type of the instance to validate is not in this set, validation for this keyword SHOULD succeed. All format values defined in this section apply to strings, but a format value can be specified to apply to any instance types defined in the data model defined in the core JSON Schema specification¹.

Implementations SHOULD provide assertion behavior for the format values defined by this document² and MUST refuse to process any schema which contains a format value it doesn't support.

In addition to the assertion behavior, this keyword also produces its value as an annotation.

Implementations:

SHOULD provide validation for each format attribute defined in this document;
are encouraged to provide validation for format attributes listed in the {{format-registry}};
MAY support format values not defined in this document or listed in the registry, but such support MUST be configurable and disabled by default;
SHOULD use a common parsing library or a well-known regular expression for each format;
SHOULD clearly document any limitations regarding format validation.

The requirement for validation of format values in general is limited to syntactic checking; implementations SHOULD NOT attempt to send an email, connect to a URL, or otherwise check the existence of an entity identified by a format instance.

Format Registry {#format-registry}

In addition to the formats defined by this document, JSON Schema also maintains a registry of formats defined by other specifications and organizations. As of the publication of this document, the format registry can be found at https://github.com/json-schema-org/json-schema-spec/blob/main/specs/registries/format.json.

Implementations SHOULD support the formats listed in this registry as if they were defined by this document.

Custom `format` Values

Implementations MAY support custom format values. Save for agreement between parties, schema authors SHALL NOT expect a peer implementation to support such custom format values.

Defined Formats

Dates, Times, and Duration

These attributes apply to string instances.

Date and time format names are derived from RFC 9557, section 4.1 which extends RFC 3339, section 5.6. The duration format is from ISO 8601 as formalized into ABNF by RFC 3339 Appendix A.

date-time: A string instance is valid against this attribute if it is a valid representation of the "date-time-ext" rule in RFC 9557
date: A string instance is valid against this attribute if it is a valid representation according to the "full-date" ABNF rule in RFC 3339
time: A string instance is valid against this attribute if it is a valid representation according to the "full-time" ABNF rule in RFC 3339
duration: A string instance is valid against this attribute if it is a valid representation according to the "duration" ABNF rule in RFC 3339 Appendix A

Implementations MAY support additional attributes using the other format names defined anywhere in that RFC. Implementations SHOULD NOT define extension attributes with any name matching an RFC 3339, RFC 9557, or ISO 8601 format unless it validates according to the rules of that format.³

Email Addresses

These attributes apply to string instances.

A string instance is valid against these format values if it is a valid Internet email address as follows:

email: As defined by the "Mailbox" ABNF rule in RFC 5321, section 4.1.2.
idn-email: As defined by the extended "Mailbox" ABNF rule in RFC 6531, section 3.3. Note that all strings valid against the "email" attribute are also valid against the "idn-email" attribute.

Hostnames

These attributes apply to string instances.

A string instance is valid against these attributes if it is a valid representation for an Internet hostname as follows:

hostname: As defined by RFC 1123, section 2.1, including host names produced using the Punycode algorithm specified in RFC 5891, section 4.4.
idn-hostname: As defined by either RFC 1123 as for hostname, or an internationalized hostname as defined by RFC 5890, section 2.3.2.3. Note that all strings valid against the "hostname" attribute are also valid against the "idn-hostname" attribute.

IP Addresses

These attributes apply to string instances.

A string instance is valid against these attributes if it is a valid representation of an IP address as follows:

ipv4: An IPv4 address according to the "dotted-quad" ABNF syntax as defined in RFC 2673, section 3.2.
ipv6: An IPv6 address as defined in RFC 4291, section 2.2.

Resource Identifiers These attributes apply to string instances.

uri: A string instance is valid against this attribute if it is a valid IRI, according to RFC 3987.
uri-reference: A string instance is valid against this attribute if it is a valid URI Reference (either a URI or a relative-reference), according to RFC 3986.
iri: A string instance is valid against this attribute if it is a valid IRI, according to RFC 3987.
iri-reference: A string instance is valid against this attribute if it is a valid IRI Reference (either an IRI or a relative-reference), according to RFC 3987.
uuid: A string instance is valid against this attribute if it is a valid string representation of a UUID, according to RFC 4122.

Note that all valid URIs are valid IRIs, and all valid URI References are also valid IRI References.

Note also that the "uuid" format is for plain UUIDs, not UUIDs in URNs. An example is "f81d4fae-7dec-11d0-a765-00a0c91e6bf6". For UUIDs as URNs, use the "uri" format, with a "pattern" regular expression of "^urn:uuid:" to indicate the URI scheme and URN namespace.

uri-template

This attribute applies to string instances.

A string instance is valid against this attribute if it is a valid URI Template (of any level), according to RFC 6570.

Note that URI Templates may be used for IRIs; there is no separate IRI Template specification.

JSON Pointers

These attributes apply to string instances.

json-pointer: A string instance is valid against this attribute if it is a valid JSON string representation of a JSON Pointer, according to RFC 6901, section 5.
relative-json-pointer: A string instance is valid against this attribute if it is a valid Relative JSON Pointer. To allow for both absolute and relative JSON Pointers, use anyOf or oneOf to indicate support for either format.

regex

This attribute applies to string instances.

A regular expression, which SHOULD be valid according to the ECMA-262 regular expression dialect.

Implementations that validate formats MUST accept at least the subset of ECMA-262 defined in {{regexinterop}}, and SHOULD accept all valid ECMA-262 expressions.

Keywords for the Contents of String-Encoded Data {#content}

Foreword

Annotations defined in this section indicate that an instance contains non-JSON data encoded in a JSON string.

These properties provide additional information required to interpret JSON data as rich multimedia documents. They describe the type of content, how it is encoded, and/or how it may be validated. They do not function as validation assertions; a malformed string-encoded document MUST NOT cause the containing instance to be considered invalid.

Implementation Requirements

Due to security and performance concerns, as well as the open-ended nature of possible content types, implementations MUST NOT automatically decode, parse, and/or validate the string contents. Applications are expected to use these annotations to invoke the appropriate libraries separately.

All keywords in this section apply only to strings, and have no effect on other data types.

`contentEncoding`

If the instance value is a string, this property defines that the string SHOULD be interpreted as encoded binary data and applications wishing to decode it SHOULD do so using the encoding named by this property.

Possible values indicating base 16, 32, and 64 encodings with several variations are listed in RFC 4648. Additionally, sections 6.7 and 6.8 of RFC 2045 provide encodings used in MIME. This keyword is derived from MIME's Content-Transfer-Encoding header, which was designed to map binary data into ASCII characters. It is not related to HTTP's Content-Encoding header, which is used to encode (e.g. compress or encrypt) the content of HTTP request and responses.

As "base64" is defined in both RFCs, the definition from RFC 4648 SHOULD be assumed unless the string is specifically intended for use in a MIME context. Note that all of these encodings result in strings consisting only of 7-bit ASCII characters. Therefore, this keyword has no meaning for strings containing characters outside of that range.

If this keyword is absent, but contentMediaType is present, this indicates that the encoding is the identity encoding, meaning that no transformation was needed in order to represent the content in a UTF-8 string.

The value of this property MUST be a string.

`contentMediaType`

If the instance is a string, this property indicates the media type of the contents of the string. If contentEncoding is present, this property describes the decoded string.

The value of this property MUST be a string, which MUST be a media type, as defined by RFC 2046.

`contentSchema`

If the instance is a string, and if contentMediaType is present, this keyword's subschema describes the structure of the string.

This keyword MAY be used with any media type that can be mapped into JSON Schema's data model. Specifying such mappings is outside of the scope of this specification.

The value of this property MUST be a valid JSON schema. The subschema is produced as an annotation.

Since contentMediaType is required to provide instruction on how to interpret string content, contentSchema SHOULD NOT produce an annotation if contentMediaType is not present.

Note that evaluating the contentSchema subschema in-place (i.e. as part of its parent schema) will ensure that it is correctly processed. Independent use of the extracted subschema (as returned in an annotation) is only safe if the subschema is an embedded resource which defines both a $schema and an absolute IRI $id.[^7]

[^7] Processing a non-resource subschema in place will ensure that any references (e.g. $ref) are always resolved properly. This isn't a problem when the subschema is itself a resource. See #1381 for several examples where processing this subschema independently can cause $ref resolution failure.

Example

Here is an example schema, illustrating the use of contentEncoding and contentMediaType:

{
  "type": "string",
  "contentEncoding": "base64",
  "contentMediaType": "image/png"
}

Instances described by this schema are expected to be strings, and their values should be interpretable as base64-encoded PNG images.

Another example:

{
  "type": "string",
  "contentMediaType": "text/html"
}

Instances described by this schema are expected to be strings containing HTML, using whatever character set the JSON string was decoded into. Per section 8.1 of RFC 8259, outside of an entirely closed system, this MUST be UTF-8.

This example describes a JWT that is MACed using the HMAC SHA-256 algorithm, and requires the "iss" and "exp" fields in its claim set.

{
  "type": "string",
  "contentMediaType": "application/jwt",
  "contentSchema": {
    "type": "array",
    "minItems": 2,
    "prefixItems": [
      {
        "const": {
          "typ": "JWT",
          "alg": "HS256"
        }
       },
      {
        "type": "object",
        "required": ["iss", "exp"],
        "properties": {
          "iss": {"type": "string"},
          "exp": {"type": "integer"}
        }
      }
    ]
  }
}

Note that contentEncoding does not appear. While the application/jwt media type makes use of base64url encoding, that is defined by the media type, which determines how the JWT string is decoded into a list of two JSON data structures: first the header, and then the payload. Since the JWT media type ensures that the JWT can be represented in a JSON string, there is no need for further encoding or decoding.

Keywords for Basic Meta-Data Annotations {#annotations}

These general-purpose annotation keywords provide commonly used information for documentation and user interface display purposes. They are not intended to form a comprehensive set of features. Rather, additional keywords can be defined for more complex annotation-based applications.

`title` and `description`

The value of both of these keywords MUST be a string.

Both of these keywords can be used to decorate a user interface with information about the data produced by this user interface. A title will preferably be short, whereas a description will provide explanation about the purpose of the instance described by this schema.

`default`

There are no restrictions placed on the value of this keyword. When multiple occurrences of this keyword are applicable to a single sub-instance, implementations SHOULD remove duplicates.

This keyword can be used to supply a default JSON value associated with a particular schema. It is RECOMMENDED that a default value be valid against the associated schema.

`deprecated`

The value of this keyword MUST be a boolean. When multiple occurrences of this keyword are applicable to a single sub-instance, applications SHOULD consider the instance location to be deprecated if any occurrence specifies a true value.

If deprecated has a value of boolean true, it indicates that applications SHOULD refrain from usage of the declared property. It may mean the property is going to be removed in the future.

A root schema containing deprecated with a value of true indicates that the entire resource being described may be removed in the future.

The deprecated keyword applies to each instance location to which the schema object containing the keyword successfully applies. This can result in scenarios where every array item or object property is deprecated even though the containing array or object is not.

Omitting this keyword has the same behavior as a value of false.

`readOnly` and `writeOnly`

The value of these keywords MUST be a boolean. When multiple occurrences of these keywords are applicable to a single sub-instance, the resulting behavior SHOULD be as for a true value if any occurrence specifies a true value, and SHOULD be as for a false value otherwise.

If readOnly has a value of boolean true, it indicates that the corresponding value in the instance is managed exclusively by the owning authority, and attempts by an application to modify the value are expected to be ignored or rejected by that owning authority.

An instance document that is marked as readOnly for the entire document may be ignored if sent to the owning authority, or may result in an error, at the authority's discretion.

If writeOnly has a value of boolean true, it indicates that the value is never present when the instance is retrieved from the owning authority. It can be present when sent to the owning authority to update or create the document (or the resource it represents), but it will not be included in any updated or newly created version of the instance.

An instance document that is marked as writeOnly for the entire document may be returned as a blank document of some sort, or may produce an error upon retrieval, or have the retrieval request ignored, at the authority's discretion.

For example, readOnly would be used to mark a database-generated serial number as read-only, while writeOnly would be used to mark a password input field.

These keywords can be used to assist in user interface instance generation. In particular, an application MAY choose to use a widget that hides input values as they are typed for write-only fields.

Omitting these keywords has the same behavior as values of false.

`examples`

The value of this keyword MUST be an array. There are no restrictions placed on the values within the array. When multiple occurrences of this keyword are applicable to a single sub-instance, implementations MUST provide a flat array of all values rather than an array of arrays.

This keyword can be used to provide sample JSON values associated with a particular schema, for the purpose of illustrating usage. It is RECOMMENDED that these values be valid against the associated schema.

Implementations MAY use the value(s) of default, if present, as an additional example. If examples is absent, default MAY still be used in this manner.

Security Considerations {#security}

JSON Schema Validation assumes all the security considerations listed in the JSON Schema Core specification.

JSON Schema Validation allows the use of Regular Expressions, which have numerous different (often incompatible) implementations. Some implementations allow the embedding of arbitrary code, which is outside the scope of JSON Schema and MUST NOT be permitted. Regular expressions can often also be crafted to be extremely expensive to compute (with so-called "catastrophic backtracking"), resulting in a denial-of-service attack.

Implementations that support validating or otherwise evaluating instance string data based on contentEncoding and/or contentMediaType are at risk of evaluating data in an unsafe way based on misleading information. Applications can mitigate this risk by only performing such processing when a relationship between the schema and instance is established (e.g., they share the same authority).

Processing a media type or encoding is subject to the security considerations of that media type or encoding. For example, the security considerations of RFC 4329 Scripting Media Types apply when processing JavaScript or ECMAScript encoded within a JSON string.

%appendix% Acknowledgments

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 Log⁴

draft-next
- Use IRIs instead of URIs
- Move "minContains" and "maxContains" to the applicator vocabulary (see also that changelog)
- Remove the optional automatic second-pass validation of "content*" keywords
- Clarify that "contentSchema"'s value is a schema just like any other subschema
draft-bhutton-json-schema-validation-01
- Improve and clarify the minContains keyword explanation
- Remove the use of "production" in favour of "ABNF rule"
draft-bhutton-json-schema-validation-00
- Correct email format RFC reference to 5321 instead of 5322
- Clarified the set and meaning of contentEncoding values
- Reference ECMA-262, 11th edition for regular expression support
- Split format into an annotation only vocabulary and an assertion vocabulary
- Clarify deprecated when applicable to arrays
draft-handrews-json-schema-validation-02
- Grouped keywords into formal vocabularies
- Update format implementation requirements in terms of vocabularies
- By default, format MUST NOT be validated, although validation can be enabled
- A vocabulary declaration can be used to require format validation
- Moved definitions to the core spec as $defs
- Moved applicator keywords to the core spec
- Renamed the array form of dependencies to dependentRequired, moved the schema form to the core spec
- Specified all content* keywords as annotations, not assertions
- Added contentSchema to allow applying a schema to a string-encoded document
- Also allow RFC 4648 encodings in contentEncoding
- Added minContains and maxContains
- Update RFC reference for nhostname" and "idn-hostname"
- Add "uuid" and "duration" formats
draft-handrews-json-schema-validation-01
- This draft is purely a clarification with no functional changes
- Provided the general principle behind ignoring annotations under not and similar cases
- Clarified if/then/else validation interactions
- Clarified if/then/else behavior for annotation
- Minor formatting and cross-referencing improvements
draft-handrews-json-schema-validation-00
- Added if/then/else
- Classify keywords as assertions or annotations per the core spec
- Warn of possibly removing dependencies in the future
- Grouped validation keywords into sub-sections for readability
- Moved readOnly from hyper-schema to validation meta-data
- Added writeOnly
- Added string-encoded media section, with former hyper-schema media keywords
- Restored "regex" format (removal was unintentional)
- Added "date" and "time" formats, and reserved additional RFC 3339 format names
- I18N formats: "iri", "iri-reference", "idn-hostname", "idn-email"
- Clarify that "json-pointer" format means string encoding, not URI fragment
- Fixed typo that inverted the meaning of minimum and exclusiveMinimum
- Move format syntax references into Normative References
- JSON is a normative requirement
draft-wright-json-schema-validation-01
- Standardized on hyphenated format names with full words ("uriref" becomes "uri-reference")
- Add the formats "uri-template" and "json-pointer"
- Changed exclusiveMaximum/exclusiveMinimum from boolean modifiers of maximum/minimum to independent numeric fields.
- Split the additionalItems/items into two sections
- Reworked properties/patternProperties/additionalProperties definition
- Added examples keyword
- Added contains keyword
- Allow empty required and dependencies arrays
- Fixed type reference to primitive types
- Added const keyword
- Added propertyNames keyword
draft-wright-json-schema-validation-00
- Added additional security considerations
- Removed reference to "latest version" meta-schema, use numbered version instead
- Rephrased many keyword definitions for brevity
- Added "uriref" format that also allows relative URI references
draft-fge-json-schema-validation-00
- Initial draft.
- Salvaged from draft v3.
- Redefine the required keyword.
- Remove extends, disallow
- Add anyOf, allOf, oneOf, not, definitions, minProperties, maxProperties.
- dependencies member values can no longer be single strings; at least one element is required in a property dependency array.
- Rename divisibleBy to multipleOf.
- type arrays can no longer have schemas; remove any as a possible value.
- Rework the format section; make support optional.
- `format": remove attributes "phone", "style", "color"; rename "ip-address" to "ipv4"; add references for all attributes.
- Provide algorithms to calculate schema(s) for array/object instances.
- Add interoperability considerations.

Authors' Addresses

Author	Company	Email	URI
Austin Wright (editor)		aaa@bzfx.net
Ben Hutton (editor)	Postman	ben@jsonschema.dev	https://jsonschema.dev

Footnotes

Note that the type keyword in this specification defines an "integer" type which is not part of the data model. Therefore a format attribute can be limited to numbers, but not specifically to integers. However, a numeric format can be used alongside the type keyword with a value of "integer", or it could be explicitly defined to always pass if the number is not an integer, which produces essentially the same behavior as only applying to integers. ↩
Assertion behavior is called out very explicitly because it is a departure from previous iterations of this specification. Previously, format was an annotation-only keyword by default and implementations that supported assertion were required to offer some configuration that allowed users to explicitly enable assertion. Assertion is now a requirement in order to meet user expectations. See json-schema-org/json-schema-spec #1520 for more. ↩
There is not currently consensus on the need for supporting all RFC 3339 formats, so this approach of reserving the namespace will encourage experimentation without committing to the entire set. Either the format implementation requirements will become more flexible in general, or these will likely either be promoted to fully specified attributes or dropped. ↩
This section to be removed before leaving Internet-Draft status. ↩

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