path: root/doc/rfc/rfc7159.txt

Internet Engineering Task Force (IETF)                      T. Bray, Ed.
Request for Comments: 7159                                  Google, Inc.
Obsoletes: 4627, 7158                                         March 2014
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/rfc7159.

















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Copyright Notice

   Copyright (c) 2014 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.

























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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.




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   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



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   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





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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.







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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 [RFC7159], Section 12.

   Interoperability considerations:  Described in [RFC7159]

   Published specification:  [RFC7159]

   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.








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   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.















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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>.






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   [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.














































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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.






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   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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