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rfc:rfc4627

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.

Crockford Informational [Page 1] RFC 4627 JSON July 2006

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

Crockford Informational [Page 2] RFC 4627 JSON July 2006

 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.

Crockford Informational [Page 3] RFC 4627 JSON July 2006

       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".

Crockford Informational [Page 4] RFC 4627 JSON July 2006

       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.

Crockford Informational [Page 5] RFC 4627 JSON July 2006

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

Crockford Informational [Page 6] RFC 4627 JSON July 2006

 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
    douglas@crockford.com
 Intended usage: COMMON
 Restrictions on usage: none
 Author:
    Douglas Crockford
    douglas@crockford.com
 Change controller:
    Douglas Crockford
    douglas@crockford.com

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]

Crockford Informational [Page 7] RFC 4627 JSON July 2006

      }
 }
 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.

Crockford Informational [Page 8] RFC 4627 JSON July 2006

 [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: douglas@crockford.com

Crockford Informational [Page 9] RFC 4627 JSON July 2006

Full Copyright Statement

 Copyright (C) The Internet Society (2006).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Crockford Informational [Page 10]

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