JSON Formatter & Validator — Format, Validate & Minify JSON Free

JSON — JavaScript Object Notation — is the dominant data interchange format in modern software. Originally derived from JavaScript object literal syntax, JSON was standardised in RFC 4627 (2006) and later in the current ECMA-404 and RFC 8259 standards. Today it is the default format for REST APIs, configuration files, database documents (MongoDB, Firestore), server-to-browser communication, and data exports from virtually every major SaaS platform.

Raw JSON from an API response typically arrives as a single unbroken line — optimised for transmission size rather than human readability. When you need to understand the structure of a response, debug an integration, review a configuration, or communicate data structure to a colleague, formatted JSON is essential. A well-indented JSON document reveals its hierarchical structure — which keys are nested inside which objects, which values are arrays, and where the boundaries between records fall — at a glance.

ToolsVenue's JSON Formatter uses JavaScript's native JSON.parse() to validate the input (the same parser used by every modern browser and Node.js) and JSON.stringify() with your chosen indentation to produce the formatted output. This means the formatter is not only accurate — it uses the reference implementation — but also guarantees that the output is syntactically correct JSON, not an approximation.

The JSON specification (ECMA-404) is deliberately strict to ensure consistent parsing across all languages and platforms. Several common mistakes produce invalid JSON:

Single quotes instead of double quotes: JSON requires all strings — both keys and values — to be enclosed in double quotes. {'name': 'Alice'} is not valid JSON. {"name": "Alice"} is.

Trailing commas: JSON does not allow a comma after the last item in an object or array. [1, 2, 3,] is invalid. [1, 2, 3] is correct. This is the single most common error when hand-editing JSON.

Unquoted keys: Unlike JavaScript object literals, JSON requires keys to be quoted strings. {name: "Alice"} is invalid; {"name": "Alice"} is correct.

JavaScript-specific values: undefined, NaN, Infinity, and -Infinity are valid JavaScript values but are not part of the JSON specification. If these appear in a JSON payload, it indicates a serialisation error.

Comments: JSON does not support comments of any kind. Neither // single-line nor /* multi-line */ comments are valid. If you need comments in config files, consider JSONC (JSON with Comments) or YAML instead.

When ToolsVenue's formatter encounters invalid JSON, it displays the exact error message from the browser's JSON parser, including the character position where the error occurs — making it straightforward to locate and fix the problem.

The 'Sort keys alphabetically' option reorders the properties of every JSON object in the document into alphabetical order. This is particularly useful in two scenarios:

Comparing JSON structures: When you have two JSON documents that should be equivalent but were generated at different times or by different systems, key order may differ even when the data is the same. Sorting both documents alphabetically before comparison ensures equivalent properties appear at the same position, making differences immediately visible.

Canonical representation: In applications where JSON must be cryptographically signed or hashed, consistent key ordering is essential — the same data must always produce the same byte sequence. Alphabetically sorted JSON provides a deterministic, canonical form.

Note that JSON objects are technically unordered collections — the specification does not guarantee key order. Most parsers preserve insertion order in practice, but relying on key order for programmatic logic is not recommended.