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rfc:rfc7158

Internet Engineering Task Force (IETF) T. Bray, Ed. Request for Comments: 7158 Google, Inc. Obsoletes: 4627 March 2013 Category: Standards Track ISSN: 2070-1721

   The JavaScript Object Notation (JSON) Data Interchange Format

Abstract

 JavaScript Object Notation (JSON) is a lightweight, text-based,
 language-independent data interchange format.  It was derived from
 the ECMAScript Programming Language Standard.  JSON defines a small
 set of formatting rules for the portable representation of structured
 data.
 This document removes inconsistencies with other specifications of
 JSON, repairs specification errors, and offers experience-based
 interoperability guidance.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7158.

Bray Standards Track [Page 1] RFC 7158 JSON March 2013

Copyright Notice

 Copyright (c) 2013 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
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.
 This document may contain material from IETF Documents or IETF
 Contributions published or made publicly available before November
 10, 2008.  The person(s) controlling the copyright in some of this
 material may not have granted the IETF Trust the right to allow
 modifications of such material outside the IETF Standards Process.
 Without obtaining an adequate license from the person(s) controlling
 the copyright in such materials, this document may not be modified
 outside the IETF Standards Process, and derivative works of it may
 not be created outside the IETF Standards Process, except to format
 it for publication as an RFC or to translate it into languages other
 than English.

Bray Standards Track [Page 2] RFC 7158 JSON March 2013

Table of Contents

 1. Introduction ....................................................3
    1.1. Conventions Used in This Document ..........................4
    1.2. Specifications of JSON .....................................4
    1.3. Introduction to This Revision ..............................4
 2. JSON Grammar ....................................................4
 3. Values ..........................................................5
 4. Objects .........................................................6
 5. Arrays ..........................................................6
 6. Numbers .........................................................6
 7. Strings .........................................................8
 8. String and Character Issues .....................................9
    8.1. Character Encoding .........................................9
    8.2. Unicode Characters .........................................9
    8.3. String Comparison ..........................................9
 9. Parsers ........................................................10
 10. Generators ....................................................10
 11. IANA Considerations ...........................................10
 12. Security Considerations .......................................11
 13. Examples ......................................................12
 14. Contributors ..................................................13
 15. References ....................................................13
    15.1. Normative References .....................................13
    15.2. Informative References ...................................13
 Appendix A. Changes from RFC 4627 .................................15

1. Introduction

 JavaScript Object Notation (JSON) is a text format for the
 serialization of structured data.  It is derived from the object
 literals of JavaScript, as defined in the ECMAScript Programming
 Language Standard, Third Edition [ECMA-262].
 JSON can represent four primitive types (strings, numbers, booleans,
 and null) and two structured types (objects and arrays).
 A string is a sequence of zero or more Unicode characters [UNICODE].
 Note that this citation references the latest version of Unicode
 rather than a specific release.  It is not expected that future
 changes in the UNICODE specification will impact the syntax of JSON.
 An object is an unordered collection of zero or more name/value
 pairs, where a name is a string and a value is a string, number,
 boolean, null, object, or array.
 An array is an ordered sequence of zero or more values.

Bray Standards Track [Page 3] RFC 7158 JSON March 2013

 The terms "object" and "array" come from the conventions of
 JavaScript.
 JSON's design goals were for it to be minimal, portable, textual, and
 a subset of JavaScript.

1.1. Conventions Used in This Document

 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 [RFC2119].
 The grammatical rules in this document are to be interpreted as
 described in [RFC5234].

1.2. Specifications of JSON

 This document updates [RFC4627], which describes JSON and registers
 the media type "application/json".
 A description of JSON in ECMAScript terms appears in Version 5.1 of
 the ECMAScript specification [ECMA-262], Section 15.12.  JSON is also
 described in [ECMA-404].
 All of the specifications of JSON syntax agree on the syntactic
 elements of the language.

1.3. Introduction to This Revision

 In the years since the publication of RFC 4627, JSON has found very
 wide use.  This experience has revealed certain patterns, which,
 while allowed by its specifications, have caused interoperability
 problems.
 Also, a small number of errata have been reported (see RFC Errata IDs
 607 [Err607] and 3607 [Err3607]).
 This document's goal is to apply the errata, remove inconsistencies
 with other specifications of JSON, and highlight practices that can
 lead to interoperability problems.

2. JSON Grammar

 A JSON text is a sequence of tokens.  The set of tokens includes six
 structural characters, strings, numbers, and three literal names.
 A JSON text is a serialized value.  Note that certain previous
 specifications of JSON constrained a JSON text to be an object or an

Bray Standards Track [Page 4] RFC 7158 JSON March 2013

 array.  Implementations that generate only objects or arrays where a
 JSON text is called for will be interoperable in the sense that all
 implementations will accept these as conforming JSON texts.
    JSON-text = ws value ws
 These are the six structural characters:
    begin-array     = ws %x5B ws  ; [ left square bracket
    begin-object    = ws %x7B ws  ; { left curly bracket
    end-array       = ws %x5D ws  ; ] right square bracket
    end-object      = ws %x7D ws  ; } right curly bracket
    name-separator  = ws %x3A ws  ; : colon
    value-separator = ws %x2C ws  ; , comma
 Insignificant whitespace is allowed before or after any of the six
 structural characters.
    ws = *(
            %x20 /              ; Space
            %x09 /              ; Horizontal tab
            %x0A /              ; Line feed or New line
            %x0D )              ; Carriage return

3. Values

 A JSON value MUST be an object, array, number, or string, or one of
 the following three literal names:
    false null true
 The literal names MUST be lowercase.  No other literal names are
 allowed.
    value = false / null / true / object / array / number / string
    false = %x66.61.6c.73.65   ; false
    null  = %x6e.75.6c.6c      ; null
    true  = %x74.72.75.65      ; true

Bray Standards Track [Page 5] RFC 7158 JSON March 2013

4. Objects

 An object structure is represented as a pair of curly brackets
 surrounding zero or more name/value pairs (or members).  A name is a
 string.  A single colon comes after each name, separating the name
 from the value.  A single comma separates a value from a following
 name.  The names within an object SHOULD be unique.
    object = begin-object [ member *( value-separator member ) ]
             end-object
    member = string name-separator value
 An object whose names are all unique is interoperable in the sense
 that all software implementations receiving that object will agree on
 the name-value mappings.  When the names within an object are not
 unique, the behavior of software that receives such an object is
 unpredictable.  Many implementations report the last name/value pair
 only.  Other implementations report an error or fail to parse the
 object, and some implementations report all of the name/value pairs,
 including duplicates.
 JSON parsing libraries have been observed to differ as to whether or
 not they make the ordering of object members visible to calling
 software.  Implementations whose behavior does not depend on member
 ordering will be interoperable in the sense that they will not be
 affected by these differences.

5. Arrays

 An array structure is represented as square brackets surrounding zero
 or more values (or elements).  Elements are separated by commas.
 array = begin-array [ value *( value-separator value ) ] end-array
 There is no requirement that the values in an array be of the same
 type.

6. Numbers

 The representation of numbers is similar to that used in most
 programming languages.  A number is represented in base 10 using
 decimal digits.  It contains an integer component that may be
 prefixed with an optional minus sign, which may be followed by a
 fraction part and/or an exponent part.  Leading zeros are not
 allowed.
 A fraction part is a decimal point followed by one or more digits.

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 An exponent part begins with the letter E in upper or lower case,
 which may be followed by a plus or minus sign.  The E and optional
 sign are followed by one or more digits.
 Numeric values that cannot be represented in the grammar below (such
 as Infinity and NaN) are not permitted.
    number = [ minus ] int [ frac ] [ exp ]
    decimal-point = %x2E       ; .
    digit1-9 = %x31-39         ; 1-9
    e = %x65 / %x45            ; e E
    exp = e [ minus / plus ] 1*DIGIT
    frac = decimal-point 1*DIGIT
    int = zero / ( digit1-9 *DIGIT )
    minus = %x2D               ; -
    plus = %x2B                ; +
    zero = %x30                ; 0
 This specification allows implementations to set limits on the range
 and precision of numbers accepted.  Since software that implements
 IEEE 754-2008 binary64 (double precision) numbers [IEEE754] is
 generally available and widely used, good interoperability can be
 achieved by implementations that expect no more precision or range
 than these provide, in the sense that implementations will
 approximate JSON numbers within the expected precision.  A JSON
 number such as 1E400 or 3.141592653589793238462643383279 may indicate
 potential interoperability problems, since it suggests that the
 software that created it expects receiving software to have greater
 capabilities for numeric magnitude and precision than is widely
 available.
 Note that when such software is used, numbers that are integers and
 are in the range [-(2**53)+1, (2**53)-1] are interoperable in the
 sense that implementations will agree exactly on their numeric
 values.

Bray Standards Track [Page 7] RFC 7158 JSON March 2013

7. Strings

 The representation of strings is similar to conventions used in the C
 family of programming languages.  A string begins and ends with
 quotation marks.  All Unicode characters may be placed within the
 quotation marks, except for the characters that must be escaped:
 quotation mark, reverse solidus, and the control characters (U+0000
 through U+001F).
 Any character may be escaped.  If the character is in the Basic
 Multilingual Plane (U+0000 through U+FFFF), then it may be
 represented as a six-character sequence: a reverse solidus, followed
 by the lowercase letter u, followed by four hexadecimal digits that
 encode the character's code point.  The hexadecimal letters A though
 F can be upper or lower case.  So, for example, a string containing
 only a single reverse solidus character may be represented as
 "\u005C".
 Alternatively, there are two-character sequence escape
 representations of some popular characters.  So, for example, a
 string containing only a single reverse solidus character may be
 represented more compactly as "\\".
 To escape an extended character that is not in the Basic Multilingual
 Plane, the character is represented as a 12-character sequence,
 encoding the UTF-16 surrogate pair.  So, for example, a string
 containing only the G clef character (U+1D11E) may be represented as
 "\uD834\uDD1E".
    string = quotation-mark *char quotation-mark
    char = unescaped /
        escape (
            %x22 /          ; "    quotation mark  U+0022
            %x5C /          ; \    reverse solidus U+005C
            %x2F /          ; /    solidus         U+002F
            %x62 /          ; b    backspace       U+0008
            %x66 /          ; f    form feed       U+000C
            %x6E /          ; n    line feed       U+000A
            %x72 /          ; r    carriage return U+000D
            %x74 /          ; t    tab             U+0009
            %x75 4HEXDIG )  ; uXXXX                U+XXXX
    escape = %x5C              ; \
    quotation-mark = %x22      ; "
    unescaped = %x20-21 / %x23-5B / %x5D-10FFFF

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8. String and Character Issues

8.1. Character Encoding

 JSON text SHALL be encoded in UTF-8, UTF-16, or UTF-32.  The default
 encoding is UTF-8, and JSON texts that are encoded in UTF-8 are
 interoperable in the sense that they will be read successfully by the
 maximum number of implementations; there are many implementations
 that cannot successfully read texts in other encodings (such as
 UTF-16 and UTF-32).
 Implementations MUST NOT add a byte order mark to the beginning of a
 JSON text.  In the interests of interoperability, implementations
 that parse JSON texts MAY ignore the presence of a byte order mark
 rather than treating it as an error.

8.2. Unicode Characters

 When all the strings represented in a JSON text are composed entirely
 of Unicode characters [UNICODE] (however escaped), then that JSON
 text is interoperable in the sense that all software implementations
 that parse it will agree on the contents of names and of string
 values in objects and arrays.
 However, the ABNF in this specification allows member names and
 string values to contain bit sequences that cannot encode Unicode
 characters; for example, "\uDEAD" (a single unpaired UTF-16
 surrogate).  Instances of this have been observed, for example, when
 a library truncates a UTF-16 string without checking whether the
 truncation split a surrogate pair.  The behavior of software that
 receives JSON texts containing such values is unpredictable; for
 example, implementations might return different values for the length
 of a string value or even suffer fatal runtime exceptions.

8.3. String Comparison

 Software implementations are typically required to test names of
 object members for equality.  Implementations that transform the
 textual representation into sequences of Unicode code units and then
 perform the comparison numerically, code unit by code unit, are
 interoperable in the sense that implementations will agree in all
 cases on equality or inequality of two strings.  For example,
 implementations that compare strings with escaped characters
 unconverted may incorrectly find that "a\\b" and "a\u005Cb" are not
 equal.

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9. Parsers

 A JSON parser transforms a JSON text into another representation.  A
 JSON parser MUST accept all texts that conform to the JSON grammar.
 A JSON parser MAY accept non-JSON forms or extensions.
 An implementation may set limits on the size of texts that it
 accepts.  An implementation may set limits on the maximum depth of
 nesting.  An implementation may set limits on the range and precision
 of numbers.  An implementation may set limits on the length and
 character contents of strings.

10. Generators

 A JSON generator produces JSON text.  The resulting text MUST
 strictly conform to the JSON grammar.

11. IANA Considerations

 The MIME media type for JSON text is application/json.
 Type name:  application
 Subtype name:  json
 Required parameters:  n/a
 Optional parameters:  n/a
 Encoding considerations:  binary
 Security considerations:  See [RFC7158], Section 12.
 Interoperability considerations:  Described in [RFC7158]
 Published specification:  [RFC7158]
 Applications that use this media type:
    JSON has been used to exchange data between applications written
    in all of these programming languages: ActionScript, C, C#,
    Clojure, ColdFusion, Common Lisp, E, Erlang, Go, Java, JavaScript,
    Lua, Objective CAML, Perl, PHP, Python, Rebol, Ruby, Scala, and
    Scheme.

Bray Standards Track [Page 10] RFC 7158 JSON March 2013

 Additional information:
    Magic number(s): n/a
    File extension(s): .json
    Macintosh file type code(s): TEXT
 Person & email address to contact for further information:
    IESG
    <iesg@ietf.org>
 Intended usage:  COMMON
 Restrictions on usage:  none
 Author:
    Douglas Crockford
    <douglas@crockford.com>
 Change controller:
    IESG
    <iesg@ietf.org>
 Note:  No "charset" parameter is defined for this registration.
    Adding one really has no effect on compliant recipients.

12. Security Considerations

 Generally, there are security issues with scripting languages.  JSON
 is a subset of JavaScript but excludes assignment and invocation.
 Since JSON's syntax is borrowed from JavaScript, it is possible to
 use that language's "eval()" function to parse JSON texts.  This
 generally constitutes an unacceptable security risk, since the text
 could contain executable code along with data declarations.  The same
 consideration applies to the use of eval()-like functions in any
 other programming language in which JSON texts conform to that
 language's syntax.

Bray Standards Track [Page 11] RFC 7158 JSON March 2013

13. Examples

 This is a JSON object:
    {
      "Image": {
          "Width":  800,
          "Height": 600,
          "Title":  "View from 15th Floor",
          "Thumbnail": {
              "Url":    "http://www.example.com/image/481989943",
              "Height": 125,
              "Width":  100
          },
          "Animated" : false,
          "IDs": [116, 943, 234, 38793]
        }
    }
 Its Image member is an object whose Thumbnail member is an object and
 whose IDs member is an array of numbers.
 This is a JSON array containing two objects:
    [
      {
         "precision": "zip",
         "Latitude":  37.7668,
         "Longitude": -122.3959,
         "Address":   "",
         "City":      "SAN FRANCISCO",
         "State":     "CA",
         "Zip":       "94107",
         "Country":   "US"
      },
      {
         "precision": "zip",
         "Latitude":  37.371991,
         "Longitude": -122.026020,
         "Address":   "",
         "City":      "SUNNYVALE",
         "State":     "CA",
         "Zip":       "94085",
         "Country":   "US"
      }
    ]

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 Here are three small JSON texts containing only values:
 "Hello world!"
 42
 true

14. Contributors

 RFC 4627 was written by Douglas Crockford.  This document was
 constructed by making a relatively small number of changes to that
 document; thus, the vast majority of the text here is his.

15. References

15.1. Normative References

 [IEEE754]  IEEE, "IEEE Standard for Floating-Point Arithmetic", IEEE
            Standard 754, August 2008,
            <http://grouper.ieee.org/groups/754/>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", STD 68, RFC 5234, January 2008.
 [UNICODE]  The Unicode Consortium, "The Unicode Standard",
            <http://www.unicode.org/versions/latest/>.

15.2. Informative References

 [ECMA-262] Ecma International, "ECMAScript Language Specification
            Edition 5.1", Standard ECMA-262, June 2011,
            <http://www.ecma-international.org/publications/standards/
            Ecma-262.htm>.
 [ECMA-404] Ecma International, "The JSON Data Interchange Format",
            Standard ECMA-404, October 2013,
            <http://www.ecma-international.org/publications/standards/
            Ecma-404.htm>.
 [Err3607]  RFC Errata, Errata ID 3607, RFC 3607,
            <http://www.rfc-editor.org>.

Bray Standards Track [Page 13] RFC 7158 JSON March 2013

 [Err607]   RFC Errata, Errata ID 607, RFC 607,
            <http://www.rfc-editor.org>.
 [RFC4627]  Crockford, D., "The application/json Media Type for
            JavaScript Object Notation (JSON)", RFC 4627, July 2006.

Bray Standards Track [Page 14] RFC 7158 JSON March 2013

Appendix A. Changes from RFC 4627

 This section lists changes between this document and the text in RFC
 4627.
 o  Changed the title and abstract of the document.
 o  Changed the reference to [UNICODE] to be not version specific.
 o  Added a "Specifications of JSON" section.
 o  Added an "Introduction to This Revision" section.
 o  Changed the definition of "JSON text" so that it can be any JSON
    value, removing the constraint that it be an object or array.
 o  Added language about duplicate object member names, member
    ordering, and interoperability.
 o  Clarified the absence of a requirement that values in an array be
    of the same JSON type.
 o  Applied erratum #607 from RFC 4627 to correctly align the artwork
    for the definition of "object".
 o  Changed "as sequences of digits" to "in the grammar below" in the
    "Numbers" section, and made base-10-ness explicit.
 o  Added language about number interoperability as a function of
    IEEE754, and added an IEEE754 reference.
 o  Added language about interoperability and Unicode characters and
    about string comparisons.  To do this, turned the old "Encoding"
    section into a "String and Character Issues" section, with three
    subsections: "Character Encoding", "Unicode Characters", and
    "String Comparison".
 o  Changed guidance in the "Parsers" section to point out that
    implementations may set limits on the range "and precision" of
    numbers.
 o  Updated and tidied the "IANA Considerations" section.
 o  Made a real "Security Considerations" section and lifted the text
    out of the previous "IANA Considerations" section.

Bray Standards Track [Page 15] RFC 7158 JSON March 2013

 o  Applied erratum #3607 from RFC 4627 by removing the security
    consideration that begins "A JSON text can be safely passed" and
    the JavaScript code that went with that consideration.
 o  Added a note to the "Security Considerations" section pointing out
    the risks of using the "eval()" function in JavaScript or any
    other language in which JSON texts conform to that language's
    syntax.
 o  Added a note to the "IANA Considerations" clarifying the absence
    of a "charset" parameter for the application/json media type.
 o  Changed "100" to 100 and added a boolean field, both in the first
    example.
 o  Added examples of JSON texts with simple values, neither objects
    nor arrays.
 o  Added a "Contributors" section crediting Douglas Crockford.
 o  Added a reference to RFC 4627.
 o  Moved the ECMAScript reference from Normative to Informative and
    updated it to reference ECMAScript 5.1, and added a reference to
    ECMA 404.

Author's Address

 Tim Bray (editor)
 Google, Inc.
 EMail: tbray@textuality.com

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