RFC 4627 JSON

Network Working Group                                       D. Crockford

Request for Comments: 4627                                      JSON.org

Category: Informational                                        July 2006

The application/json Media Type for JavaScript Object Notation (JSON)

Status of This Memo

  This memo provides information for the Internet community.  It does

  not specify an Internet standard of any kind.  Distribution of this

  memo is unlimited.

Copyright Notice

  Copyright (C) The Internet Society (2006).

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.

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].

  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].

  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.

  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.

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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 [RFC4234].

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 object or array.

     JSON-text = object / array

  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

           )

2.1.  Values

  A JSON value MUST be an object, array, number, or string, or one of

  the following three literal names:

     false null true

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  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

2.2.  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

2.3.  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

2.4.  Numbers

  The representation of numbers is similar to that used in most

  programming languages.  A number 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.

  Octal and hex forms are not allowed.  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 upper 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 as sequences of digits

  (such as Infinity and NaN) are not permitted.

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        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

2.5.  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 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 "\\".

  To escape an extended character that is not in the Basic Multilingual

  Plane, the character is represented as a twelve-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".

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        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

3.  Encoding

  JSON text SHALL be encoded in Unicode.  The default encoding is

  UTF-8.

  Since the first two characters of a JSON text will always be ASCII

  characters [RFC0020], it is possible to determine whether an octet

  stream is UTF-8, UTF-16 (BE or LE), or UTF-32 (BE or LE) by looking

  at the pattern of nulls in the first four octets.

          00 00 00 xx  UTF-32BE

          00 xx 00 xx  UTF-16BE

          xx 00 00 00  UTF-32LE

          xx 00 xx 00  UTF-16LE

          xx xx xx xx  UTF-8

4.  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 of numbers.

  An implementation may set limits on the length and character contents

  of strings.

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5. Generators

  A JSON generator produces JSON text.  The resulting text MUST

  strictly conform to the JSON grammar.

6. 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: 8bit if UTF-8; binary if UTF-16 or UTF-32

     JSON may be represented using UTF-8, UTF-16, or UTF-32.  When JSON

     is written in UTF-8, JSON is 8bit compatible.  When JSON is

     written in UTF-16 or UTF-32, the binary content-transfer-encoding

     must be used.

  Security considerations:

  Generally there are security issues with scripting languages.  JSON

  is a subset of JavaScript, but it is a safe subset that excludes

  assignment and invocation.

  A JSON text can be safely passed into JavaScript‘s eval() function

  (which compiles and executes a string) if all the characters not

  enclosed in strings are in the set of characters that form JSON

  tokens.  This can be quickly determined in JavaScript with two

  regular expressions and calls to the test and replace methods.

     var my_JSON_object = !(/[^,:{}\[\]0-9.\-+Eaeflnr-u \n\r\t]/.test(

            text.replace(/"(\\.|[^"\\])*"/g, ‘‘))) &&

        eval(‘(‘ + text + ‘)‘);

  Interoperability considerations: n/a

  Published specification: RFC 4627

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  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#,

     ColdFusion, Common Lisp, E, Erlang, Java, JavaScript, Lua,

     Objective CAML, Perl, PHP, Python, Rebol, Ruby, 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:

     Douglas Crockford

     [email protected]

  Intended usage: COMMON

  Restrictions on usage: none

  Author:

     Douglas Crockford

     [email protected]

  Change controller:

     Douglas Crockford

     [email protected]

7. Security Considerations

  See Security Considerations in Section 6.

8. 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"

         },

         "IDs": [116, 943, 234, 38793]

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       }

  }

  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"

     }

  ]

9. References

9.1.  Normative References

  [ECMA]    European Computer Manufacturers Association, "ECMAScript

            Language Specification 3rd Edition", December 1999,

            <http://www.ecma-international.org/publications/files/

            ecma-st/ECMA-262.pdf>.

  [RFC0020] Cerf, V., "ASCII format for network interchange", RFC 20,

            October 1969.

  [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate

            Requirement Levels", BCP 14, RFC 2119, March 1997.

  [RFC4234] Crocker, D. and P.  Overell, "Augmented BNF for Syntax

            Specifications: ABNF", RFC 4234, October 2005.

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  [UNICODE] The Unicode Consortium, "The Unicode Standard Version 4.0",

            2003, <http://www.unicode.org/versions/Unicode4.1.0/>.

Author‘s Address

  Douglas Crockford

  JSON.org

  EMail: [email protected]

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