JSON


JSON is an open standard file format and data interchange format that uses human-readable text to store and transmit data objects consisting of name–value pairs and arrays. It is a commonly used data format with diverse uses in electronic data interchange, including that of web applications with servers.
JSON is a programming language-independent data format. It was derived from JavaScript, but many modern programming languages include code to generate and parse JSON-format data. JSON filenames use the extension .json.
Douglas Crockford originally specified the JSON format in the early 2000s. He and Chip Morningstar sent the first JSON message in April 2001.

Naming and pronunciation

The 2017 international standard specifies that "JSON" is "pronounced, as in 'Jason and The Argonauts. The first edition of ECMA-404 did not address the pronunciation. Crockford said in 2011, "There's a lot of argument about how you pronounce that, but I strictly don't care."
is another common pronunciation.

Standards

After RFC 4627 had been available as its "informational" specification since 2006, JSON was first standardized in 2013, as ECMA-404. RFC 8259, published in 2017, is the current version of the Internet Standard STD 90, and it remains consistent with ECMA-404. That same year, JSON was also standardized as ISO/IEC 21778:2017. The ECMA and ISO/IEC standards describe only the allowed syntax, whereas the RFC covers some security and interoperability considerations.

History

JSON grew out of a need for a real-time server-to-browser session communication protocol without using browser plugins such as Flash or Java applets, the dominant methods used in the early 2000s.
Crockford first specified and popularized the JSON format. The acronym originated at State Software, a company cofounded by Crockford and others in March 2001. The cofounders agreed to build a system that used standard browser capabilities and provided an abstraction layer for Web developers to create stateful Web applications that had a persistent duplex connection to a Web server by holding two Hypertext Transfer Protocol connections open and recycling them before standard browser time-outs if no further data were exchanged. The cofounders had a round-table discussion and voted on whether to call the data format JSML or JSON, as well as under what license type to make it available. The JSON.org website was launched in 2001. In December 2005, Yahoo! began offering some of its Web services in JSON.
A precursor to the JSON libraries was used in a children's digital asset trading game project named Cartoon Orbit at Communities.com which used a browser side plug-in with a proprietary messaging format to manipulate DHTML elements. Upon discovery of early Ajax capabilities, digiGroups, Noosh, and others used frames to pass information into the user browsers' visual field without refreshing a Web application's visual context, realizing real-time rich Web applications using only the standard HTTP, HTML, and JavaScript capabilities of Netscape 4.0.5+ and Internet Explorer 5+. Crockford then found that JavaScript could be used as an object-based messaging format for such a system. The system was sold to Sun Microsystems, Amazon.com, and EDS.
JSON was based on a subset of the JavaScript scripting language and is commonly used with JavaScript, but it is a language-independent data format. Code for parsing and generating JSON data is readily available in many programming languages. JSON's website lists JSON libraries by language.
In October 2013, Ecma International published the first edition of its JSON standard ECMA-404. That same year, used ECMA-404 as a reference. In 2014, became the main reference for JSON's Internet uses, superseding and . In November 2017, ISO/IEC JTC 1/SC 22 published ISO/IEC 21778:2017 as an international standard. On December 13, 2017, the Internet Engineering Task Force obsoleted when it published, which is the current version of the Internet Standard STD 90.
Crockford added a clause to the JSON license stating, "The Software shall be used for Good, not Evil", in order to open-source the JSON libraries while mocking corporate lawyers and those who are overly pedantic. On the other hand, this clause led to license compatibility problems of the JSON license with other open-source licenses since open-source software and free software usually imply no restrictions on the purpose of use.

Syntax

The following example shows a possible JSON representation describing a person.

Character encoding

Although Crockford originally asserted that JSON is a strict subset of JavaScript and ECMAScript, his specification actually allows valid JSON documents that are not valid JavaScript; JSON allows the Unicode line terminators and to appear unescaped in quoted strings, while ECMAScript 2018 and older do not. This is a consequence of JSON disallowing only "control characters". For maximum portability, these characters are backslash-escaped.
JSON exchange in an open ecosystem must be encoded in UTF-8. The encoding supports the full Unicode character set, including those characters outside the Basic Multilingual Plane. However, if escaped, those characters must be written using UTF-16 surrogate pairs. For example, to include the Emoji character in JSON:


Or:


JSON became a strict subset of ECMAScript as of the language's 2019 revision.

Data types

JSON's basic data types are:
  • Number: a signed decimal number that may contain a fractional part and may use exponential E notation but cannot include non-numbers such as NaN. The format makes no distinction between integer and floating-point. JavaScript uses IEEE-754 double-precision floating-point format for all its numeric values, but other languages implementing JSON may encode numbers differently.
  • String: a sequence of zero or more Unicode characters. Strings are delimited with double quotation marks and support a backslash escaping syntax.
  • Boolean: either of the values true or false
  • Array: an ordered list of zero or more elements, each of which may be of any type. Arrays use square bracket notation with comma-separated elements.
  • Object: a collection of name–value pairs where the names are strings. The current ECMA standard states, "The JSON syntax does not impose any restrictions on the strings used as names, does not require that name strings be unique, and does not assign any significance to the ordering of name/value pairs." Objects are delimited with curly brackets and use commas to separate each pair, while within each pair, the colon ":" character separates the key or name from its value.
  • null: an empty value, using the word null
Whitespace is allowed and ignored around or between syntactic elements. Four specific characters are considered whitespace for this purpose: space, horizontal tab, line feed, and carriage return. In particular, the byte order mark must not be generated by a conforming implementation. JSON does not provide syntax for comments.
Early versions of JSON required that a valid JSON text must consist of only an object or an array type, which could contain other types within them. This restriction was dropped in, where a JSON text was redefined as any serialized value.
Numbers in JSON are agnostic with regard to their representation within programming languages. While this allows for numbers of arbitrary precision to be serialized, it may lead to portability issues. For example, since no differentiation is made between integer and floating-point values, some implementations may treat 42, 42.0, and 4.2E+1 as the same number, while others may not. The JSON standard makes no requirements regarding implementation details such as overflow, underflow, loss of precision, rounding, or signed zeros, but it does recommend expecting no more than IEEE 754 binary64 precision for "good interoperability". There is no inherent precision loss in serializing a machine-level binary representation of a floating-point number into a human-readable decimal representation and back; there exist published algorithms to do this conversion exactly and optimally.
Comments were intentionally excluded from JSON. In 2012, Douglas Crockford described his design decision thus: "I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability."
JSON disallows "trailing commas", a comma after the last value inside a data structure. Trailing commas are a common feature of [|JSON derivatives] to improve ease of use.

Interoperability

describes certain aspects of JSON syntax that, while legal per the specifications, can cause interoperability problems.
  • Certain JSON implementations only accept JSON texts representing an object or an array. For interoperability, applications interchanging JSON should transmit messages that are objects or arrays.
  • The specifications allow JSON objects that contain multiple members with the same name. The behavior of implementations processing objects with duplicate names is unpredictable. For interoperability, applications should avoid duplicate names when transmitting JSON objects.
  • The specifications specifically say that the order of members in JSON objects is not significant. For interoperability, applications should avoid assigning meaning to member ordering even if the parsing software makes that ordering visible.
  • While the specifications place no limits on the magnitude or precision of JSON number literals, the widely used JavaScript implementation stores them as IEEE754 "binary64" quantities. For interoperability, applications should avoid transmitting numbers that cannot be represented in this way, for example, 1E400 or 3.141592653589793238462643383279.
  • While the specifications do not constrain the character encoding of the Unicode characters in a JSON text, the vast majority of implementations assume UTF-8 encoding; for interoperability, applications should always and only encode JSON messages in UTF-8.
  • The specifications do not forbid transmitting byte sequences that incorrectly represent Unicode characters. For interoperability, applications should transmit messages containing no such byte sequences.
  • The specification does not constrain how applications go about comparing Unicode strings. For interoperability, applications should always perform such comparisons code unit by code unit.
In 2015, the IETF published, describing the "I-JSON Message Format", a restricted profile of JSON that constrains the syntax and processing of JSON to avoid, as much as possible, these interoperability issues.