JSON Repair — Fix LLM-Mangled JSON

trailing commas · single quotes · unquoted keys · smart quotes · JS comments · BOM

Paste broken JSON (or paste an LLM response that contains JSON mixed with prose — the tool extracts the JSON block). The right panel shows the repaired output and a change log lists every fix applied. Best-effort: for truly mangled output (truncated mid-token, mixed encodings), some recoveries fail.

Broken JSON

Repaired

Paste JSON to repair.

Change log

How to repair JSON

Paste broken JSON (or paste an LLM response that contains JSON mixed with prose — the tool extracts the JSON block).
The right panel shows the repaired output. A change log below lists every fix applied ("removed trailing comma on line 12", "wrapped unquoted key name in quotes").
If the repair confidence is low, the banner says Best-effort repair — review before using.
Copy the result, or Format to jump straight to json-formatter with the cleaned output.

What it fixes

Trailing commas after the last item in arrays / objects.
Single quotes around strings and keys → double quotes.
Unquoted keys ({name: 1}) → quoted keys.
Smart quotes (curly “ ” from word processors) → straight quotes.
JS-style comments (// and /* */) — stripped.
BOM (byte order mark) at the start of a file — stripped.
Prose around JSON ("here's the JSON: {...}") — the JSON block is extracted.

FAQ

Why is this a "best effort"?

Some breakage is unrecoverable — for example, a truncated string with a missing closing quote, or a number formatted as "1,234" where the comma is the thousands separator. The change log shows what was fixed; if the result still doesn't parse, you'll need to fix the rest manually.

Will it handle JSON5?

Mostly — JSON5 (comments, trailing commas, unquoted keys, single quotes) is a superset of what this tool fixes. Hex numbers and explicit + signs aren't supported.

Why did my LLM output extract incorrectly?

If your LLM put multiple JSON snippets in one response (e.g. two code fences), the tool grabs the first object/array span only. Split the response by hand before pasting.

Will it work offline?

Yes — after the page loads. The repair runs locally on your browser.