Pasting a minified API response and getting back something a human can scan. Catching syntax errors — trailing commas, unquoted keys, smart quotes — with the exact line/column the parser tripped on. Stripping whitespace before pasting JSON into a context where size matters (URL params, env vars, config files). Confirming your hand-written JSON is valid before piping it into another tool.

JSON ≠ JavaScript object literal. Keys must be in double quotes. Single quotes, unquoted keys, and trailing commas all fail. If you've got JS object literals, run them through a converter first. Smart quotes from copy-paste. Word processors and chat apps love to "helpfully" replace " with " / " . Those aren't valid JSON delimiters. JSON has no comments. If your "JSON" has // or /* */ , it's actually JSONC (used by VS Code config) — strip those before parsing. Numbers larger than 2⁵³. JavaScript can't represent integers above 9007199254740992 exactly. Twitter snowflake IDs and similar should be quoted as strings.

Formateur JSON

Formatez, validez et minifiez du JSON instantanément. Les erreurs sont signalées avec ligne et colonne.

Entrée

Sortie

Saisissez une entrée ci-dessus pour voir le résultat.

What is this for?

JSON travels minified — every byte counts when an API response is being shipped. But minified JSON is unreadable. This tool round-trips through the browser's native JSON.parse / JSON.stringify to produce indented, copy-able output, validate the structure, or strip whitespace back out. Nothing is uploaded; everything happens in the page.

When to use it

Pasting a minified API response and getting back something a human can scan.
Catching syntax errors — trailing commas, unquoted keys, smart quotes — with the exact line/column the parser tripped on.
Stripping whitespace before pasting JSON into a context where size matters (URL params, env vars, config files).
Confirming your hand-written JSON is valid before piping it into another tool.

Common gotchas

JSON ≠ JavaScript object literal. Keys must be in double quotes. Single quotes, unquoted keys, and trailing commas all fail. If you've got JS object literals, run them through a converter first.
Smart quotes from copy-paste. Word processors and chat apps love to "helpfully" replace " with " / ". Those aren't valid JSON delimiters.
JSON has no comments. If your "JSON" has // or /* */, it's actually JSONC (used by VS Code config) — strip those before parsing.
Numbers larger than 2⁵³. JavaScript can't represent integers above 9007199254740992 exactly. Twitter snowflake IDs and similar should be quoted as strings.