JSON Stringify Tool

Turning a loose JavaScript object into a clean, properly quoted JSON string is a constant need when you are moving data from code into a config file, a test fixture, or an API request body. JSON Stringify does exactly that: paste an object and it returns a valid, indented JSON string.

What sets it apart from a strict parser is tolerance for the way developers actually write objects. It accepts relaxed JavaScript syntax — unquoted keys, single quotes, trailing commas — and produces strict, double-quoted JSON from it, so you can copy an object straight out of your editor without first hand-fixing every quote.

You control the indentation, anywhere from compact single-line output to a generously spaced eight-space layout, which is handy whether you are minifying for a request or making a fixture readable.

The tool parses your input and re-serialises it with the spacing you select, so it functions as a formatter with an adjustable indent. Two spaces is the prevailing convention in JavaScript projects, four is common elsewhere, and zero produces the minified single-line form used for transmission.

Indentation has no effect on meaning — a parser treats all three as identical — so the choice is entirely about who reads it next. Human-readable indentation for anything committed to a repository or reviewed in a diff; minified for anything sent over a network, where the whitespace is pure payload.

The round trip through a parser also normalises the document, which is why the output may differ from your input in ways beyond whitespace: resolved escapes, canonical number formatting, and duplicate keys collapsed to their last occurrence.

In code, converting an object to JSON is lossy in ways that catch people out. Undefined values, functions, and symbol keys are omitted entirely from objects and become null inside arrays. Dates are converted to ISO strings and do not come back as dates. Map, Set, BigInt, and circular references either throw or serialise to something useless.

A custom serialiser hook can control this, and a matching hook on the parsing side can restore richer types — that pairing is how libraries transmit dates and other structures safely. Where an object defines its own conversion method, the serialiser calls it, which is exactly why dates behave as they do.

Key order in output follows insertion order for string keys, which makes serialisation useful for producing a stable diff between two documents — but only if both were built the same way. For genuinely canonical output, where a byte-identical result matters for hashing or signing, a dedicated canonicalisation library is required rather than the standard serialiser.