JSON Stringify Online

It's a real serializer with real, sometimes-surprising rules, and this page shows the values it drops as well as the ones it converts. undefined values, functions and Symbols disappear entirely — an object key holding any of them is simply omitted from the output, and an array holding one becomes null in that slot instead of being removed (arrays keep their length). A Date instance calls its own toJSON() method, which returns an ISO string. NaN and Infinity have no JSON representation and both become the literal null. A BigInt throws a TypeError — JSON.stringify refuses to serialize one rather than silently rounding it. A circular reference (an object that contains itself, directly or through a chain) also throws, with a "Converting circular structure to JSON" message. Key order is preserved exactly as insertion order, and this page reproduces every one of these behaviors rather than approximating them.

It's JSON.stringify()'s third parameter, and it controls indentation: omitted or 0 (the default on this page) produces the tightest possible output with no extra whitespace anywhere — which is what JSON.stringify(value) actually does when you call it with no third argument, the single most common call shape in real code. A number from 1–10 inserts that many spaces per nesting level; the string "\t" (this page's Tab option) inserts a literal tab per level instead. This page defaults to compact specifically because that's the true default of the function it's modeling — a page that pretty-printed first would be showing you JSON.stringify(value, null, 2)'s output while claiming to demonstrate JSON.stringify(value), which is a different call.

Switch Mode to Unstringify and paste the stringified value — either the full quoted-and-escaped string JSON.stringify produced (with its outer quotes) or just the escaped content without them, both are accepted. The page parses one layer of escaping and, if what's left is itself valid JSON, parses and pretty-prints that too, reporting how many top-level keys it found; if the unescaped content isn't JSON, you get the plain unescaped text back instead. A value that was stringified twice (nested inside another JSON.stringify call) needs two passes — run Unstringify, then run it again on the result to peel the second layer.

Because you stringified a value that was ALREADY a JSON string, so the serializer escaped the escapes: a document that was already text like "{\"a\":1}" gets its own backslashes doubled and its quotes escaped again on a second pass, producing \"{\\\"a\\\":1}\". This is a genuinely common accident — logging a payload with JSON.stringify(JSON.stringify(x)) instead of JSON.stringify(x), or a webhook provider that stringifies its body twice before sending it. Run the result through Unstringify twice (once per accidental layer) to get back to the real document, or check the code path that produced the value for a duplicate stringify call.

Three pages model three different things, and this is the one that models the JavaScript FUNCTION itself: what JSON.stringify(value, replacer, space) actually returns for a given value, including the parts it drops (undefined, functions) and the parts it converts (Date, NaN), plus the reverse operation. [JSON to String](/json-to-string) is the page for a complete, ready-to-paste string LITERAL in a language of your choice — Python, Java, C#, SQL and more, not just JavaScript, and always including the delimiters. [JSON Escape](/json-escape) is the narrowest of the three: it returns only the escaped BODY of a string, no delimiters, no JavaScript-specific semantics, for when you already have your own quotes to drop it into. If the question is "what would JSON.stringify(x) actually return," this page. If it's "give me a Python/Java/SQL string literal," JSON to String. If it's "just escape this text for inside a string I already have," JSON Escape.