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

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]

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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: douglas@crockford.com

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