The application/json Media Type for JavaScript Object Notation (JSON)
Registers the application/json media type for JavaScript Object Notation.
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>.
@misc{rfc4627,
series = {Request for Comments},
number = 4627,
howpublished = {RFC 4627},
publisher = {RFC Editor},
doi = {10.17487/RFC4627},
url = {https://www.rfc-editor.org/info/rfc4627},
author = {D. Crockford},
title = {{The application/json Media Type for JavaScript Object Notation (JSON)}},
pagetotal = 10,
year = 2006,
month = jul,
} RFC text
Contents
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. 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 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. 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". 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. 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 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] } } 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. [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 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. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgement Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA).
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§1What Is JSON
JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It is derived from the object literals of JavaScript as defined in the ECMAScript Programming Language Standard.
JSON can represent four primitive types: strings (sequences of Unicode characters), numbers, booleans (true and false), and null. It also has two structured types: objects (unordered collections of name/value pairs where names are strings and values can be any JSON type) and arrays (ordered sequences of zero or more values).
The design goals for JSON were to be minimal (with a small set of formatting rules), portable (language-independent), textual (human-readable), and a subset of JavaScript (so JSON can be safely parsed with JavaScript's eval() function).
JSON is a simple format that describes data using curly brackets for containers and square brackets for lists. It can store text, numbers, true/false, and null (empty).
§2JSON Grammar and Syntax
A JSON text is a sequence of tokens consisting of six structural characters, strings, numbers, and three literal names. JSON data must be either a serialized object or an array.
The six structural characters are: [ (begin array), ] (end array), { (begin object), } (end object), : (name separator), and , (value separator). Whitespace (space, tab, line feed, and carriage return) is allowed before or after these characters.
A value must be either an object, array, number, string, or one of three literal names: false, null, or true (always lowercase). An object is surrounded by curly brackets and contains zero or more name/value pairs separated by commas. An array is surrounded by square brackets and contains zero or more values separated by commas.
Numbers consist of an optional minus sign, an integer component, an optional fraction part (decimal point followed by digits), and an optional exponent part. Octal and hexadecimal forms, leading zeros, and special values like Infinity or NaN are not permitted.
JSON uses curly brackets for objects, square brackets for arrays, and colons to separate a name from a value. Numbers, text, true/false, and null are the simple values you can store.
§3Strings and Character Encoding
A string in JSON is a sequence of zero or more Unicode characters enclosed in quotation marks. Characters that must be escaped are: the quotation mark, reverse solidus (backslash), and control characters (U+0000 through U+001F).
Any character may be escaped using a backslash followed by specific codes: \" for quotation mark, \\ for backslash, \/ for solidus, \b for backspace, \f for form feed, \n for line feed, \r for carriage return, \t for tab, or \u followed by four hexadecimal digits for other Unicode characters.
JSON text MUST be encoded in Unicode with UTF-8 as the default encoding. The RFC provides a method to detect whether an octet stream uses UTF-8, UTF-16 (big-endian or little-endian), or UTF-32 (big-endian or little-endian) by examining the pattern of null bytes in the first four octets.
JSON uses backslash escape codes to include special characters in text, like \n for a line break or \" for a quote mark. JSON is always Unicode text, usually in UTF-8 format.
§4Parsers and Generators
A JSON parser transforms a JSON text into another representation. A compliant parser MUST accept all texts that conform to the JSON grammar. A parser may accept non-JSON forms or extensions, and it may set limits on the size of texts, the maximum depth of nesting, the range of numbers, and the length and character contents of strings.
A JSON generator produces JSON text. The resulting text MUST strictly conform to the JSON grammar. Generators are responsible for ensuring syntactically correct output.
A parser is a program that reads JSON and turns it into something the program can use. A generator is a program that creates JSON.
§5MIME Media Type Registration
The MIME media type for JSON is application/json. The type name is 'application' and the subtype is 'json'. There are no required or optional parameters.
JSON encoding considerations depend on the Unicode encoding used: JSON is 8-bit compatible when written in UTF-8, but when using UTF-16 or UTF-32, the binary content-transfer-encoding must be used.
The specification notes that JSON applications include ActionScript, C, C#, ColdFusion, Common Lisp, E, Erlang, Java, JavaScript, Lua, Objective CAML, Perl, PHP, Python, Rebol, Ruby, and Scheme.
application/json is the official label that tells email systems and web browsers that a file contains JSON data. Files can use the .json extension.
§6Security Considerations
The RFC notes general security issues with scripting languages. JSON is a subset of JavaScript, but a safe subset that excludes assignment and invocation, preventing malicious code execution.
A JSON text can be safely processed by JavaScript's eval() function (which compiles and executes a string) if all non-string characters are valid JSON tokens. The RFC provides a verification method using regular expressions: the implementation tests against forbidden characters, removes legitimate string content, and safely evaluates the result.
JSON is safe to process through JavaScript because it doesn't allow code execution like regular JavaScript does. Special characters in text are protected with backslash escapes.