JSON formatter & validator — with the exact error line

Paste the JSON into the left box and press Format. The formatter checks it, then prints it on the right with one key per line and the indentation you picked (2 spaces, 4 spaces or tabs). Press Minify for the shortest one-line version instead.

Press Format. If the JSON is invalid, the red box names the line and column where it breaks, shows that line with a caret under the problem, and says what is wrong in plain words, for example "Trailing comma before } is not allowed" or "Expected ',' or '}' after a value. A comma may be missing."

A comma after the last item, single quotes instead of double quotes, keys without quotes, comments (JSON has none), a missing comma between two values, and values like undefined or NaN. These are all valid in JavaScript but not in JSON, which is why copied code often fails.

Yes. The formatter is JavaScript that runs in your own browser. The JSON is never uploaded to HostKarle or anywhere else. You can disconnect from the internet after the page loads and it still works.

It orders every object's keys alphabetically, at every level. That makes two JSON files easy to compare, for example with our text compare tool, because the same keys end up on the same lines.

Files of several megabytes format in well under a second on a normal laptop, because it uses the browser's own JSON engine. Very large files (50 MB and more) depend on your device's memory.

Use json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE). To check whether a string is valid JSON in PHP 8.3, call json_validate($string); in older versions decode it and check json_last_error().