The JavaScript Object Notation (JSON) Data Interchange Format
RFC 8259

Internet Engineering Task Force (IETF)                      T. Bray, Ed.
Request for Comments: 8259                                    Textuality
Obsoletes: 7159                                            December 2017
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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8259.

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Copyright Notice

   Copyright (c) 2017 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
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   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 . . . . . . . . . . . . . .   5
   2.  JSON Grammar  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Values  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   4.  Objects . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   5.  Arrays  . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   7.  Strings . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  String and Character Issues . . . . . . . . . . . . . . . . .   9
     8.1.  Character Encoding  . . . . . . . . . . . . . . . . . . .   9
     8.2.  Unicode Characters  . . . . . . . . . . . . . . . . . . .  10
     8.3.  String Comparison . . . . . . . . . . . . . . . . . . . .  10
   9.  Parsers . . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   10. Generators  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  12
   13. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  14
     14.2.  Informative References . . . . . . . . . . . . . . . . .  14
   Appendix A.  Changes from RFC 7159  . . . . . . . . . . . . . . .  16
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  16
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  16

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", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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

1.2.  Specifications of JSON

   This document replaces [RFC7159].  [RFC7159] obsoleted [RFC4627],
   which originally described JSON and registered the media type
   "application/json".

   JSON is also described in [ECMA-404].

   The reference to ECMA-404 in the previous sentence is normative, not
   with the usual meaning that implementors need to consult it in order
   to understand this document, but to emphasize that there are no
   inconsistencies in the definition of the term "JSON text" in any of
   its specifications.  Note, however, that ECMA-404 allows several
   practices that this specification recommends avoiding in the
   interests of maximal interoperability.

   The intent is that the grammar is the same between the two documents,
   although different descriptions are used.  If there is a difference
   found between them, ECMA and the IETF will work together to update
   both documents.

   If an error is found with either document, the other should be
   examined to see if it has a similar error; if it does, it should be
   fixed, if possible.

   If either document is changed in the future, ECMA and the IETF will
   work together to ensure that the two documents stay aligned through
   the change.

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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 that, while
   allowed by its specifications, have caused interoperability problems.

   Also, a small number of errata have been reported regarding RFC 4627
   (see RFC Errata IDs 607 [Err607] and 3607 [Err3607]) and regarding
   RFC 7159 (see RFC Errata IDs 3915 [Err3915], 4264 [Err4264], 4336
   [Err4336], and 4388 [Err4388]).

   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
   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

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   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

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

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   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.

   An exponent part begins with the letter E in uppercase or lowercase,
   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

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      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 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.

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 through
   F can be uppercase or lowercase.  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 "\\".

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   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

8.  String and Character Issues

8.1.  Character Encoding

   JSON text exchanged between systems that are not part of a closed
   ecosystem MUST be encoded using UTF-8 [RFC3629].

   Previous specifications of JSON have not required the use of UTF-8
   when transmitting JSON text.  However, the vast majority of JSON-
   based software implementations have chosen to use the UTF-8 encoding,
   to the extent that it is the only encoding that achieves
   interoperability.

   Implementations MUST NOT add a byte order mark (U+FEFF) to the
   beginning of a networked-transmitted 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.

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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.

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.

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11.  IANA Considerations

   The 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 RFC 8259, Section 12

   Interoperability considerations:  Described in RFC 8259

   Published specification:  RFC 8259

   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.

   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>

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   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 most JSON texts (but
   not all; certain characters such as U+2028 LINE SEPARATOR and U+2029
   PARAGRAPH SEPARATOR are legal in JSON but not JavaScript).  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.

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.

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   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"
        }
      ]

   Here are three small JSON texts containing only values:

   "Hello world!"

   42

   true

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14.  References

14.1.  Normative References

   [ECMA-404] Ecma International, "The JSON Data Interchange Format",
              Standard ECMA-404,
              <http://www.ecma-international.org/publications/
              standards/Ecma-404.htm>.

   [IEEE754]  IEEE, "IEEE Standard for Floating-Point Arithmetic",
              IEEE 754.

   [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>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <https://www.rfc-editor.org/info/rfc3629>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard",
              <http://www.unicode.org/versions/latest/>.

14.2.  Informative References

   [ECMA-262] Ecma International, "ECMAScript Language Specification",
              Standard ECMA-262, Third Edition, December 1999,
              <http://www.ecma-international.org/publications/files/
              ECMA-ST-ARCH/
              ECMA-262,%203rd%20edition,%20December%201999.pdf>.

   [Err3607]  RFC Errata, Erratum ID 3607, RFC 4627,
              <https://www.rfc-editor.org/errata/eid3607>.

   [Err3915]  RFC Errata, Erratum ID 3915, RFC 7159,
              <https://www.rfc-editor.org/errata/eid3915>.

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   [Err4264]  RFC Errata, Erratum ID 4264, RFC 7159,
              <https://www.rfc-editor.org/errata/eid4264>.

   [Err4336]  RFC Errata, Erratum ID 4336, RFC 7159,
              <https://www.rfc-editor.org/errata/eid4336>.

   [Err4388]  RFC Errata, Erratum ID 4388, RFC 7159,
              <https://www.rfc-editor.org/errata/eid4388>.

   [Err607]   RFC Errata, Erratum ID 607, RFC 4627,
              <https://www.rfc-editor.org/errata/eid607>.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627,
              DOI 10.17487/RFC4627, July 2006,
              <https://www.rfc-editor.org/info/rfc4627>.

   [RFC7159]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
              2014, <https://www.rfc-editor.org/info/rfc7159>.

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Appendix A.  Changes from RFC 7159

   This section lists changes between this document and the text in
   RFC 7159.

   o  Section 1.2 has been updated to reflect the removal of a JSON
      specification from ECMA-262, to make ECMA-404 a normative
      reference, and to explain the particular meaning of "normative".

   o  Section 1.3 has been updated to reflect errata filed against
      RFC 7159, not RFC 4627.

   o  Section 8.1 was changed to require the use of UTF-8 when
      transmitted over a network.

   o  Section 12 has been updated to increase the precision of the
      description of the security risk that follows from using the
      ECMAScript "eval()" function.

   o  Section 14.1 has been updated to include ECMA-404 as a normative
      reference.

   o  Section 14.2 has been updated to remove ECMA-404, update the
      version of ECMA-262, and refresh the errata list.

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.

Author's Address

   Tim Bray (editor)
   Textuality

   Email: tbray@textuality.com

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