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INTERNET STANDARD
Errata Exist
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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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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