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JavaScript Object Notation (JSON, pronounced /ˈdʒeɪsən/; also /ˈdʒeɪˌsɒn/[note 1]) is an open-standard file format that uses human-readable text to transmit data objects consisting of attribute–value pairs and array data types (or any other serializable value). It is a very common data format, with a diverse range of applications, such as serving as replacement for XML in AJAX systems.

JSON is a language-independent data format. It was derived from JavaScript, but many modern programming languages include code to generate and parse JSON-format data. The official Internet media type for JSON is application/json. JSON filenames use the extension .json.

Douglas Crockford originally specified the JSON format in the early 2000s. JSON was first standardized in 2013, as ECMA-404. The latest JSON format standard was published in 2017 as RFC 8259, and remains consistent with ECMA-404. That same year, JSON was also standardized as ISO/IEC 21778:2017. The ECMA and ISO standards describes only the allowed syntax, whereas the RFC covers some security and interoperability considerations.

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 a 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 values, each of which may be of any type. Arrays use square bracket notation with comma-separated elements.

  • Object: an unordered collection of name–value pairs where the names (also called keys) are strings. Objects are intended to represent associative arrays, where each key is unique within an object. 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 (values and punctuation, but not within a string value). 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 (though it may be accepted when parsing JSON). JSON does not provide syntax for comments.

Early versions of JSON (such as specified by RFC 4627) required that a valid JSON text must consist of only an object or an array type, which could contain other types within them.

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