 The JSON logo is aMöbius strip | |
| Filename extension | .json |
|---|---|
| Internet media type | application/json |
| Type code | TEXT |
| Uniform Type Identifier (UTI) | public.json |
| Type of format | Data interchange |
| Extended from | JavaScript |
| Standard | STD 90 (RFC 8259),ECMA-404,ISO/IEC 21778:2017 |
| Open format? | Yes |
| Website | json |
JSON (JavaScript Object Notation, pronounced/ˈdʒeɪsən/ or/ˈdʒeɪˌsɒn/) is anopen standard file format anddata interchange format that useshuman-readable text to store and transmit data objects consisting ofname–value pairs andarrays (or otherserializable values). It is a commonly used data format with diverse uses inelectronic data interchange, including that ofweb applications withservers.
JSON is alanguage-independent data format. It was derived fromJavaScript, but many modernprogramming languages include code to generate andparse JSON-format data. JSON filenames use the extension.json.
Douglas Crockford originally specified the JSON format in the early 2000s.[1] He andChip Morningstar sent the first JSON message in April 2001.
The 2017international standard (ECMA-404 and ISO/IEC 21778:2017) specifies that "JSON" is "pronounced/ˈdʒeɪ.sən/, as in 'Jason and TheArgonauts'".[2][3] The first (2013) edition of ECMA-404 did not address the pronunciation.[4] TheUNIX and Linux System Administration Handbook states, "Douglas Crockford, who named and promoted the JSON format, says it's pronounced like the name Jason. But somehow, 'JAY-sawn'[note 1] seems to have become more common in the technical community."[5] Crockford said in 2011, "There's a lot of argument about how you pronounce that, but I strictly don't care."[1]
After RFC 4627 had been available as its "informational" specification since 2006, JSON was first standardized in 2013, asECMA-404.[4] RFC 8259, published in 2017, is the current version of theInternet Standard STD 90, and it remains consistent with ECMA-404.[6] That same year, JSON was also standardized asISO/IEC 21778:2017.[2] TheECMA andISO/IEC standards describe only the allowed syntax, whereas the RFC covers some security and interoperability considerations.[7]
JSON grew out of a need for a real-time server-to-browser session communication protocol without using browser plugins such asFlash orJava applets, the dominant methods used in the early 2000s.[8]
Crockford first specified and popularized the JSON format.[1] 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 anabstraction layer for Web developers to create stateful Web applications that had a persistent duplex connection to a Web server by holding twoHypertext Transfer Protocol (HTTP) 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 (JavaScript Markup Language) or JSON (JavaScript Object Notation), as well as under whatlicense type to make it available. The JSON.org[9] website was launched in 2001. In December 2005,Yahoo! began offering some of itsWeb services in JSON.[10]
A precursor to the JSON libraries was used in a children's digital asset trading game project namedCartoon Orbit at Communities.com[citation needed] which used a browser side plug-in with a proprietary messaging format to manipulateDHTML elements. Upon discovery of earlyAjax 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 toSun Microsystems,Amazon.com, andEDS.
JSON was based on asubset of theJavaScript scripting language (specifically, StandardECMA-262 3rd Edition—December 1999[11]) and is commonly used with JavaScript, but it is alanguage-independent data format. Code forparsing and generating JSON data is readily available in manyprogramming languages. JSON's website lists JSONlibraries by language.
In October 2013,Ecma International published the first edition of its JSON standard ECMA-404.[4] That same year,RFC 7158 used ECMA-404 as a reference. In 2014,RFC 7159 became the main reference for JSON's Internet uses, supersedingRFC 4627 andRFC 7158 (but preserving ECMA-262 and ECMA-404 as main references). In November 2017,ISO/IEC JTC 1/SC 22 published ISO/IEC 21778:2017[2] as an international standard. On December 13, 2017, theInternet Engineering Task Force obsoletedRFC 7159 when it publishedRFC 8259, which is the current version of theInternet Standard STD 90.[12][13]
Crockford added a clause to the JSON license stating, "The Software shall be used for Good, not Evil", in order toopen-source the JSON libraries while mocking corporate lawyers and those who are overly pedantic. On the other hand, this clause led tolicense compatibility problems of the JSON license with otheropen-source licenses sinceopen-source software andfree software usually imply no restrictions on the purpose of use.[14]
The following example shows a possible JSON representation describing a person.
{"first_name":"John","last_name":"Smith","is_alive":true,"age":27,"address":{"street_address":"21 2nd Street","city":"New York","state":"NY","postal_code":"10021-3100"},"phone_numbers":[{"type":"home","number":"212 555-1234"},{"type":"office","number":"646 555-4567"}],"children":["Catherine","Thomas","Trevor"],"spouse":null}
Although Crockford originally asserted that JSON is a strict subset ofJavaScript andECMAScript,[15] his specification actually allows valid JSON documents that are not valid JavaScript; JSON allows theUnicode line terminatorsU+2028 LINE SEPARATOR andU+2029 PARAGRAPH SEPARATOR to appear unescaped in quoted strings, while ECMAScript 2018 and older do not.[16][17] 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 inUTF-8.[6] The encoding supports the full Unicode character set, including those characters outside theBasic Multilingual Plane (U+0000 to U+FFFF). However, if escaped, those characters must be written usingUTF-16 surrogate pairs. For example, to include theEmoji characterU+1F610 😐NEUTRAL FACE in JSON:
{"face":"😐"}// or{"face":"\uD83D\uDE10"}
JSON became a strict subset of ECMAScript as of the language's 2019 revision.[17][18]
JSON's basic data types are:
true orfalsenull: an empty value, using the wordnullWhitespace is allowed and ignored around or between syntactic elements (values and punctuation, but not within a string value). Four specific characters are considered whitespace for this purpose:space,horizontal tab,line feed, andcarriage return. In particular, thebyte order mark must not be generated by a conforming implementation (though it may be accepted when parsing JSON). JSON does not provide syntax forcomments.[21]
Early versions of JSON (such as specified byRFC 4627) 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 inRFC 7158, 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 ofarbitrary 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 treat42,42.0, and4.2E+1 as the same number, while others may not. The JSON standard makes no requirements regarding implementation details such asoverflow,underflow, loss of precision, rounding, orsigned zeros, but it does recommend expecting no more thanIEEE 754binary64 precision for "good interoperability". There is no inherent precision loss in serializing a machine-level binary representation of a floating-point number (like binary64) into a human-readable decimal representation (like numbers in JSON) and back since there exist published algorithms to do this exactly and optimally.[22]
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."[21]
JSON disallows "trailing commas", acomma after the last value inside a data structure.[23] Trailing commas are a common feature ofJSON derivatives to improve ease of use.[24]
RFC 8259 describes certain aspects of JSON syntax that, while legal per the specifications, can cause interoperability problems.
In 2015, the IETF published RFC 7493, 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.
While JSON provides a syntactic framework for data interchange, unambiguous data interchange also requires agreement between producer and consumer on the semantics of specific use of the JSON syntax.[25] One example of where such an agreement is necessary is the serialization of data types that are not part of the JSON standard, for example, dates andregular expressions.
The officialMIME type for JSON text isapplication/json,[26] and most modern implementations have adopted this. Legacy MIME types includetext/json,text/x-json, andtext/javascript.[27] The standard filename extension is .json.[28]
JSON Schema specifies a JSON-based format to define the structure of JSON data for validation, documentation, and interaction control. It provides a contract for the JSON data required by a given application and how that data can be modified.[29] JSON Schema is based on the concepts fromXML Schema (XSD) but is JSON-based. As in XSD, the same serialization/deserialization tools can be used both for the schema and data, and it is self-describing. It is specified in anInternet Draft at the IETF, with the latest version as of 2024 being "Draft 2020-12".[30] There are several validators available for different programming languages,[31] each with varying levels of conformance.
The JSON standard does not support objectreferences, but anIETF draft standard for JSON-based object references exists.[32]
JSON-RPC is aremote procedure call (RPC) protocol built on JSON, as a replacement forXML-RPC orSOAP. It is a simple protocol that defines only a handful of data types and commands. JSON-RPC lets a system send notifications (information to the server that does not require a response) and multiple calls to the server that can be answered out of order.
Asynchronous JavaScript and JSON (or AJAJ) refers to the samedynamic web page methodology asAjax, but instead ofXML, JSON is the data format. AJAJ is a web development technique that provides for the ability of aweb page to request new data after it has loaded into theweb browser. Typically, it renders new data from the server in response to user actions on that web page. For example, what the user types into asearch box,client-side code then sends to the server, which immediately responds with adrop-down list of matchingdatabase items.
JSON has seenad hoc usage as aconfiguration language. However, it does not supportcomments.In 2012, Douglas Crockford, JSON creator, had this to say about comments in JSON when used as a configuration language: "I know that the lack of comments makes some people sad, but it shouldn't. Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it through JSMin[33] before handing it to your JSON parser."[21]
MongoDB uses JSON-like data for itsdocument-oriented database.
Some relational databases, such as PostgreSQL and MySQL, have added support for native JSON data types. This allows developers to store JSON data directly in a relational database without having to convert it to another data format.
JSON being a subset of JavaScript can lead to the misconception that it is safe to pass JSON texts to the JavaScripteval() function. This is not safe, due to certain valid JSON texts, specifically those containingU+2028 LINE SEPARATOR orU+2029 PARAGRAPH SEPARATOR, not being valid JavaScript code until JavaScript specifications were updated in 2019, and so older engines may not support it.[34] To avoid the many pitfalls caused by executing arbitrary code from the Internet, a new function,JSON.parse(), was first added to the fifth edition of ECMAScript,[35] which as of 2017 is supported by all major browsers. For non-supported browsers, an API-compatible JavaScript library is provided byDouglas Crockford.[36] In addition, the TC39 proposal "Subsume JSON" madeECMAScript a strict JSON superset as of the language's 2019 revision.[17][18] Various JSON parser implementations have suffered fromdenial-of-service attack andmass assignment vulnerability.[37][38]
JSON is promoted as a low-overhead alternative to XML as both of these formats have widespread support for creation, reading, and decoding in the real-world situations where they are commonly used.[39] Apart from XML, examples could includeCSV andsupersets of JSON.Google Protocol Buffers can fill this role, although it is not a data interchange language.CBOR has a superset of the JSON data types, but it is not text-based. Ion is also a superset of JSON, with a wider range of primary types, annotations, comments, and allowing trailing commas.[40]
XML has been used to describe structured data and to serialize objects. Various XML-based protocols exist to represent the same kind of data structures as JSON for the same kind of data interchange purposes. Data can be encoded in XML in several ways. The most expansive form using tag pairs results in a much larger (in character count) representation than JSON, but if data is stored in attributes and 'short tag' form where the closing tag is replaced with/>, the representation is often about the same size as JSON or just a little larger. However, an XML attribute can only have a single value and each attribute can appear at most once on each element.
XML separates "data" from "metadata" (via the use of elements and attributes), while JSON does not have such a concept.
Another key difference is the addressing of values. JSON has objects with a simple "key" to "value" mapping, whereas in XML addressing happens on "nodes", which all receive a unique ID via the XML processor. Additionally, the XML standard defines a common attributexml:id, that can be used by the user, to set an ID explicitly.
XML tag names cannot contain any of the characters!"#$%&'()*+,/;<=>?@[\]^`{|}~, nor a space character, and cannot begin with-,., or a numeric digit, whereas JSON keys can (even if quotation mark and backslash must be escaped).[41]
XML values are strings ofcharacters, with no built-intype safety. XML has the concept ofschema, that permits strong typing, user-defined types, predefined tags, and formal structure, allowing for formal validation of an XML stream. JSON has several types built-in and has a similar schema concept inJSON Schema.
XML supports comments, while JSON does not.[42][21]
Support forcomments and other features have been deemed useful, which has led to several nonstandard JSONsupersets being created. Among them are HJSON,[43] HOCON, and JSON5 (which despite its name, is not the fifth version of JSON).[44][45]
YAML version 1.2 is a superset of JSON; prior versions were not strictly compatible. For example, escaping a slash/ with a backslash\ is valid in JSON, but was not valid in YAML.[46] YAML supports comments, while JSON does not.[46][44][21]
CSON ("CoffeeScript Object Notation") usessignificant indentation, unquoted keys, and assumes an outer object declaration. It was used for configuringGitHub'sAtom text editor.[47][48][49]
There is also an unrelated project calledCSON ("Cursive Script Object Notation") that is more syntactically similar to JSON.[50]
HOCON ("Human-Optimized Config Object Notation") is a format forhuman-readable data, and a superset of JSON.[51]The uses of HOCON are:
JSON5 ("JSON5 Data Interchange Format") is an extension of JSON syntax that, just like JSON, is also valid JavaScript syntax. The specification was started in 2012 and finished in 2018 with version 1.0.0.[62] The main differences to JSON syntax are:
JSON5 syntax is supported in some software as an extension of JSON syntax, for instance inSQLite.[63]
JSONC (JSON with Comments) is a subset of JSON5 used in Microsoft'sVisual Studio Code:[64]
//) and block comments (/* */)Several serialization formats have been built on or from the JSON specification. Examples include
{{cite journal}}:Cite journal requires|journal= (help)In 1996, Macromedia launches Flash technology which occupies the space left by Java and ActiveX, becoming the de facto standard for animation on the client side.
It is based on a subset of the JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999.
2017-12-13 [...] RFC published
Type: RFC - Internet Standard (December 2017; Errata); Obsoletes RFC 7159; Also known as STD 90
JSON is a subset of the object literal notation of JavaScript.
I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability. I know that the lack of comments makes some people sad, but it shouldn't. Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it throughJSMin before handing it to your JSON parser.
JSMin [2001] is a minification tool that removes comments and unnecessary whitespace from JavaScript files.
for data representation you can pick one of the following: YAML, YAMLEX, JSON, JSON5, HJSON, or even pure Python
The primary goal is: keep the semantics (tree structure; set of types; encoding/escaping) from JSON, but make it more convenient as a human-editable config file format.
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