API responses arrive as a single ten-thousand-character line, and config files fail with 'unexpected token' at a position that means nothing to humans. This tool fixes both moods.
Updated August 12, 2026, after a fresh review, with updated visuals and links.
Paste JSON below: format it readable, minify it tiny, or just validate, with errors translated into line and column numbers you can actually find.
The three errors that break JSON
Trailing commas are the classic: {'a': 1,} is legal in JavaScript but fatal in JSON. Arrays too: [1, 2,].
Single quotes don't exist in JSON: only double quotes wrap strings and keys, always, no exceptions.
Unquoted keys: {name: 'x'} is a JavaScript object, not JSON. Every key needs double quotes: {'name': 'x'}.
Worth remembering
- Validating before formatting pinpoints errors at their true position; formatting a broken file first shifts the reported line.
- Minify before pasting into environment variables or single-line config slots: it guarantees one clean line.
Frequently asked
Is it safe to paste my API response here?
Yes: parsing and formatting run fully in your browser. You can verify by turning off WiFi; the tool keeps working.
Why is my JSON invalid with a trailing comma?
Because the JSON spec is stricter than JavaScript: no trailing commas, no comments, no single quotes, and no undefined. Those four sins cause 90% of parse failures.
