About this tool
Large language models are brilliant at generating structured data, but their JSON output is often almost-right: a trailing comma before a closing brace, single quotes instead of double quotes, unquoted keys copied from JavaScript habits, explanatory text wrapped around the payload, a markdown code fence, or a response that was simply truncated mid-object when the token budget ran out. LLM JSON Repair cleans all of that in one click. Paste the messy output and the tool strips code fences and prose, converts single-quoted strings, quotes bare keys, removes trailing commas, and attempts to close unterminated strings, arrays and objects so truncated responses still parse. The repaired result is validated with the native JSON parser, pretty-printed, and ready to copy. Because everything runs locally in your browser, you can safely paste payloads that contain API keys, customer data or other sensitive content — nothing ever leaves your machine. It is ideal for anyone building agents, structured-output pipelines, or prompt-engineering workflows who needs a fast way to salvage an otherwise perfect LLM response that failed json.loads at the last comma.
How to use LLM JSON Repair
- Paste the broken JSON produced by the LLM into the input box.
- Press the Repair JSON button.
- Review the repaired, pretty-printed output and the list of fixes that were applied.
- Copy the valid JSON with the Copy button and use it in your code or pipeline.
Frequently asked questions
What kinds of errors can this tool fix?
It handles the most common LLM mistakes: trailing commas, single-quoted strings, unquoted object keys, markdown code fences, surrounding prose, comments, and truncated output with unclosed brackets or strings.
Is my data uploaded to a server?
No. All repair and validation happens entirely in your browser using JavaScript. Nothing is transmitted, logged or stored anywhere.
What if the JSON is too broken to repair?
If the structure cannot be salvaged, the tool reports the parser error position so you can fix the remaining issue manually.
Does it change my data values?
No. Repairs are purely syntactic — quotes, commas, keys and brackets. Your string values, numbers and booleans are preserved exactly.