A single missing comma, one place, is enough for a JSON parser to reject the entire document — there’s no partial success. That’s by design (it’s what makes JSON unambiguous to parse), but it means the error message is often the only clue to a problem that can otherwise take a slow visual scan to find. This tool runs the same JSON.parse every browser and Node.js use, and turns the byte offset in the error into a line number.

The four mistakes behind almost every syntax error

• A trailing comma — {"a": 1, "b": 2,}. Valid in JavaScript object literals, invalid in JSON. The single most common cause of a “valid in my editor, rejected everywhere else” JSON file, because a JS/TS file that happens to look like JSON tolerates it.
• An unquoted key — {name: "Ada"} instead of {"name": "Ada"}. Every key in JSON must be a double-quoted string, with no exception.
• Single quotes instead of double — {'name': 'Ada'}. JSON has exactly one string delimiter, and it’s the double quote.
• A missing or extra closing bracket — easy to lose track of by eye in a deeply nested document; the formatter’s indentation makes a mismatched } or ] visible immediately once the rest of the document is valid.

Format vs. minify — when each is the right output

• Format (pretty-print) — for reading, editing, diffing in version control, or pasting into documentation. The indentation is the whole point.
• Minify — for shipping. Every byte of whitespace in a JSON payload is a byte a client has to download for no benefit once a human isn’t reading it directly — API responses, config bundled into a build, anything sent over a network.

Frequently asked

Does this tool support JSON5 or JSONC (comments, trailing commas)?

No — it validates against strict JSON, the format nearly everything that consumes JSON actually requires (APIs, JSON.parse, most config loaders). JSON5 and JSONC are supersets meant for hand-edited config files specifically because they relax these rules; converting one of those to this tool’s input means stripping the comments and trailing commas first.

Why does the error line number look approximate on a one-line file?

The underlying parser reports a character offset, not a line/column pair — this tool counts newlines up to that offset to find the line. On a minified, single-line JSON document, every error will report line 1, since there’s only one line to report.

Does this tool send my JSON anywhere?

No — formatting, minifying and validating all run in your browser with the same JSON.parse/JSON.stringify built into JavaScript. Nothing is uploaded.

Can I convert this JSON to CSV?

Yes — see the CSV to JSON Converter, which converts in both directions.