Internet Engineering Task Force A. Wright, Ed.
Internet-Draft
Intended status: Informational H. Andrews, Ed.
Expires: March 19, 2020
B. Hutton, Ed.
Wellcome Sanger Institute
September 16, 2019
JSON Schema Validation: A Vocabulary for Structural Validation of JSON
draft-handrews-json-schema-validation-02
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.
Status of This Memo
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provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 19, 2020.
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Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Interoperability Considerations . . . . . . . . . . . . . . . 4
4.1. Validation of String Instances . . . . . . . . . . . . . 4
4.2. Validation of Numeric Instances . . . . . . . . . . . . . 5
4.3. Regular Expressions . . . . . . . . . . . . . . . . . . . 5
5. Meta-Schema . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. A Vocabulary for Structural Validation . . . . . . . . . . . 5
6.1. Validation Keywords for Any Instance Type . . . . . . . . 6
6.1.1. type . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1.2. enum . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1.3. const . . . . . . . . . . . . . . . . . . . . . . . . 6
6.2. Validation Keywords for Numeric Instances (number and
integer) . . . . . . . . . . . . . . . . . . . . . . . . 6
6.2.1. multipleOf . . . . . . . . . . . . . . . . . . . . . 6
6.2.2. maximum . . . . . . . . . . . . . . . . . . . . . . . 7
6.2.3. exclusiveMaximum . . . . . . . . . . . . . . . . . . 7
6.2.4. minimum . . . . . . . . . . . . . . . . . . . . . . . 7
6.2.5. exclusiveMinimum . . . . . . . . . . . . . . . . . . 7
6.3. Validation Keywords for Strings . . . . . . . . . . . . . 7
6.3.1. maxLength . . . . . . . . . . . . . . . . . . . . . . 7
6.3.2. minLength . . . . . . . . . . . . . . . . . . . . . . 8
6.3.3. pattern . . . . . . . . . . . . . . . . . . . . . . . 8
6.4. Validation Keywords for Arrays . . . . . . . . . . . . . 8
6.4.1. maxItems . . . . . . . . . . . . . . . . . . . . . . 8
6.4.2. minItems . . . . . . . . . . . . . . . . . . . . . . 8
6.4.3. uniqueItems . . . . . . . . . . . . . . . . . . . . . 8
6.4.4. maxContains . . . . . . . . . . . . . . . . . . . . . 9
6.4.5. minContains . . . . . . . . . . . . . . . . . . . . . 9
6.5. Validation Keywords for Objects . . . . . . . . . . . . . 9
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6.5.1. maxProperties . . . . . . . . . . . . . . . . . . . . 9
6.5.2. minProperties . . . . . . . . . . . . . . . . . . . . 9
6.5.3. required . . . . . . . . . . . . . . . . . . . . . . 10
6.5.4. dependentRequired . . . . . . . . . . . . . . . . . . 10
7. A Vocabulary for Semantic Content With "format" . . . . . . . 10
7.1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . 10
7.2. Implementation Requirements . . . . . . . . . . . . . . . 11
7.2.1. As an annotation . . . . . . . . . . . . . . . . . . 11
7.2.2. As an assertion . . . . . . . . . . . . . . . . . . . 12
7.2.3. Custom format attributes . . . . . . . . . . . . . . 13
7.3. Defined Formats . . . . . . . . . . . . . . . . . . . . . 13
7.3.1. Dates, Times, and Duration . . . . . . . . . . . . . 14
7.3.2. Email Addresses . . . . . . . . . . . . . . . . . . . 14
7.3.3. Hostnames . . . . . . . . . . . . . . . . . . . . . . 15
7.3.4. IP Addresses . . . . . . . . . . . . . . . . . . . . 15
7.3.5. Resource Identifiers . . . . . . . . . . . . . . . . 15
7.3.6. uri-template . . . . . . . . . . . . . . . . . . . . 16
7.3.7. JSON Pointers . . . . . . . . . . . . . . . . . . . . 16
7.3.8. regex . . . . . . . . . . . . . . . . . . . . . . . . 16
8. A Vocabulary for the Contents of String-Encoded Data . . . . 17
8.1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2. Implementation Requirements . . . . . . . . . . . . . . . 17
8.3. contentEncoding . . . . . . . . . . . . . . . . . . . . . 18
8.4. contentMediaType . . . . . . . . . . . . . . . . . . . . 18
8.5. contentSchema . . . . . . . . . . . . . . . . . . . . . . 18
8.6. Example . . . . . . . . . . . . . . . . . . . . . . . . . 19
9. A Vocabulary for Basic Meta-Data Annotations . . . . . . . . 20
9.1. "title" and "description" . . . . . . . . . . . . . . . . 21
9.2. "default" . . . . . . . . . . . . . . . . . . . . . . . . 21
9.3. "deprecated" . . . . . . . . . . . . . . . . . . . . . . 21
9.4. "readOnly" and "writeOnly" . . . . . . . . . . . . . . . 22
9.5. "examples" . . . . . . . . . . . . . . . . . . . . . . . 22
10. Security Considerations . . . . . . . . . . . . . . . . . . . 23
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1. Normative References . . . . . . . . . . . . . . . . . . 23
11.2. Informative References . . . . . . . . . . . . . . . . . 25
Appendix A. Keywords Moved from Validation to Core . . . . . . . 26
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . 26
Appendix C. ChangeLog . . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. 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.
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This specification will use the concepts, syntax, and terminology
defined by the JSON Schema core [json-schema] specification.
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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 [json-schema].
3. 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
small vocabulary of metadata keywords that can be used to annotate
the JSON instance with useful information. The Section 7 keyword is
intended primarily as an annotation, but can optionally be used as an
assertion. The Section 8 keywords are annotations for working with
documents embedded as JSON strings.
4. Interoperability Considerations
4.1. 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.
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4.2. 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.
4.3. Regular Expressions
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
[json-schema] specification.
5. Meta-Schema
The current URI for the default JSON Schema meta-schema is
<http://json-schema.org/draft/2019-09/schema>. For schema author
convenience, this meta-schema describes all vocabularies defined in
this specification and the JSON Schema Core specification, as well as
two former keywords which are reserved for a transitional period.
Individual vocabulary and vocabulary meta-schema URIs are given for
each section below. Certain vocabularies are optional to support,
which is explained in detail in the relevant sections.
Updated vocabulary and meta-schema URIs MAY be published between
specification drafts in order to correct errors. Implementations
SHOULD consider URIs dated after this specification draft and before
the next to indicate the same syntax and semantics as those listed
here.
6. A Vocabulary 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.
Meta-schemas that do not use "$vocabulary" SHOULD be considered to
require this vocabulary as if its URI were present with a value of
true.
The current URI for this vocabulary, known as the Validation
vocabulary, is: <https://json-schema.org/draft/2019-09/vocab/
validation>.
The current URI for the corresponding meta-schema is: <https://json-
schema.org/draft/2019-09/meta/validation>.
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6.1. Validation Keywords for Any Instance Type
6.1.1. type
The value of this keyword MUST be either a string or an array. If it
is an array, 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.
An instance validates if and only if the instance is in any of the
sets listed for this keyword.
6.1.2. 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.
6.1.3. const
The value of this keyword MAY be of any type, including null.
Use of this keyword is functionally equivalent to an "enum"
(Section 6.1.2) with a single value.
An instance validates successfully against this keyword if its value
is equal to the value of the keyword.
6.2. Validation Keywords for Numeric Instances (number and integer)
6.2.1. 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.
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6.2.2. 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".
6.2.3. exclusiveMaximum
The value of "exclusiveMaximum" MUST be 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".
6.2.4. 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".
6.2.5. exclusiveMinimum
The value of "exclusiveMinimum" MUST be 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".
6.3. Validation Keywords for Strings
6.3.1. 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 its
characters as defined by RFC 8259 [RFC8259].
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6.3.2. 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 its
characters as defined by RFC 8259 [RFC8259].
Omitting this keyword has the same behavior as a value of 0.
6.3.3. pattern
The value of this keyword MUST be a string. This string SHOULD be a
valid regular expression, according to the ECMA 262 regular
expression dialect.
A string instance is considered valid if the regular expression
matches the instance successfully. Recall: regular expressions are
not implicitly anchored.
6.4. Validation Keywords for Arrays
6.4.1. 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.
6.4.2. 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.
6.4.3. 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.
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Omitting this keyword has the same behavior as a value of false.
6.4.4. maxContains
The value of this keyword MUST be a non-negative integer.
An array instance is valid against "maxContains" if the number of
elements that are valid against the schema for "contains"
[json-schema] is less than, or equal to, the value of this keyword.
If "contains" is not present within the same schema object, then this
keyword has no effect.
6.4.5. minContains
The value of this keyword MUST be a non-negative integer.
An array instance is valid against "minContains" if the number of
elements that are valid against the schema for "contains"
[json-schema] is greater than, or equal to, the value of this
keyword.
A value of 0 is allowed, but is only useful for setting a range of
occurrences from 0 to the value of "maxContains". A value of 0 with
no "maxContains" causes "contains" to always pass validation.
If "contains" is not present within the same schema object, then this
keyword has no effect.
Omitting this keyword has the same behavior as a value of 1.
6.5. Validation Keywords for Objects
6.5.1. 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.
6.5.2. 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.
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6.5.3. 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.
6.5.4. 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.
7. A Vocabulary for Semantic Content With "format"
7.1. 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.
Implementations MAY treat "format" as an assertion in addition to an
annotation, and attempt to validate the value's conformance to the
specified semantics. See the Implementation Requirements below for
details.
The value of this keyword is called a format attribute. It MUST be a
string. A format attribute can 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 format attribute and instance SHOULD
succeed. All format attributes defined in this section apply to
strings, but a format attribute can be specified to apply to any
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instance types defined in the data model defined in the core JSON
Schema. [json-schema] [[CREF1: 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 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. ]]
Meta-schemas that do not use "$vocabulary" SHOULD be considered to
utilize this vocabulary as if its URI were present with a value of
false. See the Implementation Requirements below for details.
The current URI for this vocabulary, known as the Format vocabulary,
is: <https://json-schema.org/draft/2019-09/vocab/format>.
The current URI for the corresponding meta-schema is: <https://json-
schema.org/draft/2019-09/meta/format>.
7.2. Implementation Requirements
The "format" keyword functions as an annotation, and optionally as an
assertion. [[CREF2: This is due to the keyword's history, and is not
in line with current keyword design principles.]] In order to manage
this ambiguity, the "format" keyword is defined in its own separate
vocabulary, as noted above. The true or false value of the
vocabulary declaration governs the implementation requirements
necessary to process a schema that uses "format", and the behaviors
on which schema authors can rely.
7.2.1. As an annotation
The value of format MUST be collected as an annotation, if the
implementation supports annotation collection. This enables
application-level validation when schema validation is unavailable or
inadequate.
This requirement is not affected by the boolean value of the
vocabulary declaration, nor by the configuration of "format"'s
assertion behavior described in the next section. [[CREF3: Requiring
annotation collection even when the vocabulary is declared with a
value of false is atypical, but necessary to ensure that the best
practice of performing application-level validation is possible even
when assertion evaluation is not implemented. Since "format" has
always been a part of this specification, requiring implementations
to be aware of it even with a false vocabulary declaration is deemed
to not be a burden. ]]
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7.2.2. As an assertion
Regardless of the boolean value of the vocabulary declaration, an
implementation that can evaluate "format" as an assertion MUST
provide options to enable and disable such evaluation. The assertion
evaluation behavior when the option is not explicitly specified
depends on the vocabulary declaration's boolean value.
When implementing this entire specification, this vocabulary MUST be
supported with a value of false (but see details below), and MAY be
supported with a value of true.
When the vocabulary is declared with a value of false, an
implementation:
MUST NOT evaluate "format" as an assertion unless it is explicitly
configured to do so;
SHOULD provide an implementation-specific best effort validation
for each format attribute defined below;
MAY choose to implement validation of any or all format attributes
as a no-op by always producing a validation result of true;
SHOULD document its level of support for validation.
[[CREF4: This matches the current reality of implementations, which
provide widely varying levels of validation, including no validation
at all, for some or all format attributes. It is also designed to
encourage relying only on the annotation behavior and performing
semantic validation in the application, which is the recommended best
practice. ]]
When the vocabulary is declared with a value of true, an
implementation that supports this form of the vocabulary:
MUST evaluate "format" as an assertion unless it is explicitly
configured not to do so;
MUST implement syntactic validation for all format attributes
defined in this specification, and for any additional format
attributes that it recognizes, such that there exist possible
instance values of the correct type that will fail validation.
The requirement for minimal validation of format attributes is
intentionally vague and permissive, due to the complexity involved in
many of the attributes. Note in particular that the requirement is
limited to syntactic checking; it is not to be expected that an
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implementation would send an email, attempt to connect to a URL, or
otherwise check the existence of an entity identified by a format
instance. [[CREF5: The expectation is that for simple formats such
as date-time, syntactic validation will be thorough. For a complex
format such as email addresses, which are the amalgamation of various
standards and numerous adjustments over time, with obscure and/or
obsolete rules that may or may not be restricted by other
applications making use of the value, a minimal validation is
sufficient. For example, an instance string that does not contain an
"@" is clearly not a valid email address, and an "email" or
"hostname" containing characters outside of 7-bit ASCII is likewise
clearly invalid. ]]
It is RECOMMENDED that implementations use a common parsing library
for each format, or a well-known regular expression. Implementations
SHOULD clearly document how and to what degree each format attribute
is validated.
The standard core and validation meta-schema (Section 5) includes
this vocabulary in its "$vocabulary" keyword with a value of false,
since by default implementations are not required to support this
keyword as an assertion. Supporting the format vocabulary with a
value of true is understood to greatly increase code size and in some
cases execution time, and will not be appropriate for all
implementations.
7.2.3. Custom format attributes
Implementations MAY support custom format attributes. Save for
agreement between parties, schema authors SHALL NOT expect a peer
implementation to support such custom format attributes. An
implementation MUST NOT fail validation or cease processing due to an
unknown format attribute. When treating "format" as an annotation,
implementations SHOULD collect both known and unknown format
attribute values.
Vocabularies do not support specifically declaring different value
sets for keywords. Due to this limitation, and the historically
uneven implementation of this keyword, it is RECOMMENDED to define
additional keywords in a custom vocabulary rather than additional
format attributes if interoperability is desired.
7.3. Defined Formats
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7.3.1. Dates, Times, and Duration
These attributes apply to string instances.
Date and time format names are derived from RFC 3339, section 5.6
[RFC3339]. The duration format is from the ISO 8601 ABNF as given in
Appendix A of RFC 3339.
Implementations supporting formats SHOULD implement support for the
following attributes:
date-time: A string instance is valid against this attribute if it
is a valid representation according to the "date-time" production.
date: A string instance is valid against this attribute if it is a
valid representation according to the "full-date" production.
time: A string instance is valid against this attribute if it is a
valid representation according to the "full-time" production.
duration: A string instance is valid against this attribute if it is
a valid representation according to the "duration" production.
Implementations MAY support additional attributes using the other
production names defined in that section. If "full-date" or "full-
time" are implemented, the corresponding short form ("date" or "time"
respectively) MUST be implemented, and MUST behave identically.
Implementations SHOULD NOT define extension attributes with any name
matching an RFC 3339 production unless it validates according to the
rules of that production. [[CREF6: 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.
]]
7.3.2. Email Addresses
These attributes apply to string instances.
A string instance is valid against these attributes if it is a valid
Internet email address as follows:
email: As defined by RFC 5322, section 3.4.1 [RFC5322].
idn-email: As defined by RFC 6531 [RFC6531]
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Note that all strings valid against the "email" attribute are also
valid against the "idn-email" attribute.
7.3.3. 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 [RFC1123], including
host names produced using the Punycode algorithm specified in RFC
5891, section 4.4 [RFC5891].
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
[RFC5890].
Note that all strings valid against the "hostname" attribute are also
valid against the "idn-hostname" attribute.
7.3.4. 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 [RFC2673].
ipv6: An IPv6 address as defined in RFC 4291, section 2.2 [RFC4291].
7.3.5. Resource Identifiers
These attributes apply to string instances.
uri: A string instance is valid against this attribute if it is a
valid URI, according to [RFC3986].
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 [RFC3986].
iri: A string instance is valid against this attribute if it is a
valid IRI, according to [RFC3987].
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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 [RFC3987].
uuid: A string instance is valid against this attribute if it is a
valid string representation of a UUID, according to [RFC4122].
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.
7.3.6. 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 [RFC6570].
Note that URI Templates may be used for IRIs; there is no separate
IRI Template specification.
7.3.7. 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 [RFC6901].
relative-json-pointer: A string instance is valid against this
attribute if it is a valid Relative JSON Pointer
[relative-json-pointer].
To allow for both absolute and relative JSON Pointers, use "anyOf" or
"oneOf" to indicate support for either format.
7.3.8. regex
This attribute applies to string instances.
A regular expression, which SHOULD be valid according to the ECMA 262
[ecma262] regular expression dialect.
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Implementations that validate formats MUST accept at least the subset
of ECMA 262 defined in the Regular Expressions (Section 4.3) section
of this specification, and SHOULD accept all valid ECMA 262
expressions.
8. A Vocabulary for the Contents of String-Encoded Data
8.1. 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.
Meta-schemas that do not use "$vocabulary" SHOULD be considered to
require this vocabulary as if its URI were present with a value of
true.
The current URI for this vocabulary, known as the Content vocabulary,
is: <https://json-schema.org/draft/2019-09/vocab/content>.
The current URI for the corresponding meta-schema is: <https://json-
schema.org/draft/2019-09/meta/content>.
8.2. 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 by
default. This additionally supports the use case of embedded
documents intended for processing by a different consumer than that
which processed the containing document.
All keywords in this section apply only to strings, and have no
effect on other data types.
Implementations MAY offer the ability to decode, parse, and/or
validate the string contents automatically. However, it MUST NOT
perform these operations by default, and MUST provide the validation
result of each string-encoded document separately from the enclosing
document. This process SHOULD be equivalent to fully evaluating the
instance against the original schema, followed by using the
annotations to decode, parse, and/or validate each string-encoded
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document. [[CREF7: For now, the exact mechanism of performing and
returning parsed data and/or validation results from such an
automatic decoding, parsing, and validating feature is left
unspecified. Should such a feature prove popular, it may be
specified more thoroughly in a future draft. ]]
See also the Security Considerations (Section 10) sections for
possible vulnerabilities introduced by automatically processing the
instance string according to these keywords.
8.3. contentEncoding
If the instance value is a string, this property defines that the
string SHOULD be interpreted as binary data and decoded using the
encoding named by this property.
Possible values for this property are listed in RFC 2045, Sec 6.1
[RFC2045] and RFC 4648 [RFC4648]. For "base64", which is defined in
both RFCs, the definition in RFC 4648, which removes line length
limitations, SHOULD be used, as various other specifications have
mandated different lengths. Note that line lengths within a string
can be constrained using the "pattern" (Section 6.3.3) keyword.
If this keyword is absent, but "contentMediaType" is present, this
indicates that the media type could be encoded into UTF-8 like any
other JSON string value, and does not require additional decoding.
The value of this property MUST be a string.
8.4. 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 [RFC2046].
8.5. contentSchema
If the instance is a string, and if "contentMediaType" is present,
this property contains a schema which 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.
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The value of this property SHOULD be ignored if "contentMediaType" is
not present.
8.6. 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 [RFC8259], outside of an
entirely closed system, this MUST be UTF-8.
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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,
"items": [
{
"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.
9. A Vocabulary for Basic Meta-Data 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 vocabularies can be defined for more complex
annotation-based applications.
Meta-schemas that do not use "$vocabulary" SHOULD be considered to
require this vocabulary as if its URI were present with a value of
true.
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The current URI for this vocabulary, known as the Meta-Data
vocabulary, is: <https://json-schema.org/draft/2019-09/vocab/meta-
data>.
The current URI for the corresponding meta-schema is: <https://json-
schema.org/draft/2019-09/meta/meta-data>.
9.1. "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.
9.2. "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.
9.3. "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.
When the "deprecated" keyword is applied to an item in an array by
means of "items", if "items" is a single schema, the deprecation
relates to the whole array, while if "items" is an array of schemas,
the deprecation relates to the corrosponding item according to the
subschemas position.
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Omitting this keyword has the same behavior as a value of false.
9.4. "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
value of the instance is managed exclusively by the owning authority,
and attempts by an application to modify the value of this property
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.
9.5. "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.
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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.
10. Security Considerations
JSON Schema validation defines a vocabulary for JSON Schema core and
concerns all the security considerations listed there.
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 [RFC4329]
apply when processing JavaScript or ECMAScript encoded within a JSON
string.
11. References
11.1. Normative References
[ecma262] "ECMA 262 specification", <http://www.ecma-
international.org/publications/files/ECMA-ST/
Ecma-262.pdf>.
[json-schema]
Wright, A. and H. Andrews, "JSON Schema: A Media Type for
Describing JSON Documents", draft-handrews-json-schema-02
(work in progress), November 2017.
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[relative-json-pointer]
Luff, G. and H. Andrews, "Relative JSON Pointers", draft-
handrews-relative-json-pointer-01 (work in progress),
November 2017.
[RFC1123] Braden, R., Ed., "Requirements for Internet Hosts -
Application and Support", STD 3, RFC 1123,
DOI 10.17487/RFC1123, October 1989,
<https://www.rfc-editor.org/info/rfc1123>.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<https://www.rfc-editor.org/info/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2673] Crawford, M., "Binary Labels in the Domain Name System",
RFC 2673, DOI 10.17487/RFC2673, August 1999,
<https://www.rfc-editor.org/info/rfc2673>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<https://www.rfc-editor.org/info/rfc3339>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, DOI 10.17487/RFC3987,
January 2005, <https://www.rfc-editor.org/info/rfc3987>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
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[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/info/rfc5890>.
[RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891,
DOI 10.17487/RFC5891, August 2010,
<https://www.rfc-editor.org/info/rfc5891>.
[RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized
Email", RFC 6531, DOI 10.17487/RFC6531, February 2012,
<https://www.rfc-editor.org/info/rfc6531>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/info/rfc6570>.
[RFC6901] Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
"JavaScript Object Notation (JSON) Pointer", RFC 6901,
DOI 10.17487/RFC6901, April 2013,
<https://www.rfc-editor.org/info/rfc6901>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
11.2. Informative References
[RFC4329] Hoehrmann, B., "Scripting Media Types", RFC 4329,
DOI 10.17487/RFC4329, April 2006,
<https://www.rfc-editor.org/info/rfc4329>.
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Appendix A. Keywords Moved from Validation to Core
Several keywords have been moved from this document into the Core
Specification [json-schema] as of this draft, in some cases with re-
naming or other changes. This affects the following former
validation keywords:
"definitions" Renamed to "$defs" to match "$ref" and be shorter to
type. Schema vocabulary authors SHOULD NOT define a "definitions"
keyword with different behavior in order to avoid invalidating
schemas that still use the older name. While "definitions" is
absent in the single-vocabulary meta-schemas referenced by this
document, it remains present in the default meta-schema, and
implementations SHOULD assume that "$defs" and "definitions" have
the same behavior when that meta-schema is used.
"allOf", "anyOf", "oneOf", "not", "if", "then", "else",
"items", "additionalItems",
"contains", "propertyNames",
"properties", "patternProperties", "additionalProperties"
All of these keywords apply subschemas to the instance and combine
their results, without asserting any conditions of their own.
Without assertion keywords, these applicators can only cause
assertion failures by using the false boolean schema, or by
inverting the result of the true boolean schema (or equivalent
schema objects). For this reason, they are better defined as a
generic mechanism on which validation, hyper-schema, and extension
vocabularies can all be based.
"dependencies" This keyword had two different modes of behavior,
which made it relatively challenging to implement and reason
about. The schema form has been moved to Core and renamed to
"dependentSchemas", as part of the applicator vocabulary. It is
analogous to "properties", except that instead of applying its
subschema to the property value, it applies it to the object
containing the property. The property name array form is retained
here and renamed to "dependentRequired", as it is an assertion
which is a shortcut for the conditional use of the "required"
assertion keyword.
Appendix B. Acknowledgments
Thanks to Gary Court, Francis Galiegue, Kris Zyp, and Geraint Luff
for their work on the initial drafts of JSON Schema.
Thanks to Jason Desrosiers, Daniel Perrett, Erik Wilde, Ben Hutton,
Evgeny Poberezkin, Brad Bowman, Gowry Sankar, Donald Pipowitch, Dave
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Finlay, and Denis Laxalde for their submissions and patches to the
document.
Appendix C. ChangeLog
[[CREF8: This section to be removed before leaving Internet-Draft
status.]]
draft-handrews-json-schema-validation-02
* Grouped keywords into formal vocabuarlies
* 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 "hostname" 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
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* 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"
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* 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.
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* 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
Austin Wright (editor)
EMail: aaa@bzfx.net
Henry Andrews (editor)
EMail: andrews_henry@yahoo.com
Ben Hutton (editor)
Wellcome Sanger Institute
EMail: bh7@sanger.ac.uk
URI: https://jsonschema.dev
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