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Free JSON Repair Online - TestMu AI (Formerly LambdaTest)
This free tool allows you to repair malformed JSON in your browser with no upload.
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Auto-fixes quotes, commas, comments, and truncated braces.
Repair JSON
What is JSON Repair?
JSON Repair is a utility that rewrites almost-JSON text into documents that parse under RFC 8259. It fixes syntax mistakes such as trailing commas, single quotes, unquoted keys, comments, Python literals, markdown fences, and truncated braces. TestMu AI runs the repair in your browser so fixtures and API payloads stay on the page during processing.
After repair, continue with the JSON Validator or JSON Prettify tools when you need a second check or a different view of the same payload.
How do you use this JSON Repair tool?
Paste broken JSON, repair it locally, then copy or download the pretty-printed result. All processing happens in your browser. No data is uploaded for the repair step itself.
- Paste broken JSON: Enter text in the input box, click Sample, upload a .json or .txt file, or load text from a URL.
- Repair JSON: Leave Auto Update on for live repairs, or click Repair JSON to refresh the output once.
- Review pretty-printed output: Confirm keys and values match what you expect after the automatic formatting step.
- Copy or download: Use the output icons to copy the repaired JSON or save repaired.json for fixtures and tests.
What is the difference between JSON repair and JSON validation?
Repair and validation answer different questions. Repair asks whether almost-JSON can be rewritten into parseable JSON. Validation asks whether a document already conforms to the grammar.
| JSON repair | JSON validation |
|---|---|
| Accepts invalid input and rewrites common syntax mistakes. | Accepts a candidate document and reports pass or fail. |
| Output is intended to be parseable JSON you can copy. | Output is a verdict, and often an error location. |
| Best for LLM fences, trailing commas, and quote style. | Best for confirming fixtures before you ship them. |
What features does this JSON Repair tool include?
The widget focuses on the syntax fixes developers hit when cleaning configs, API logs, and model output. Here are the features of this JSON Repair tool:
- Trailing and missing commas: Removes illegal trailing commas and inserts missing commas between values when the structure is clear.
- Quote and key fixes: Converts single quotes to double quotes and wraps unquoted object keys.
- Comment and fence stripping: Drops // and /* */ comments plus markdown code fences around JSON blocks.
- Python and truncated repair: Maps True, False, and None to JSON literals and closes open braces when output is cut off.
- Browser-only workflow: Clear, Copy, Upload, Load from URL, Sample, Download, and Auto Update run without a repair API.
What are common use cases for JSON Repair?
Teams use JSON repair whenever a strict parser rejects text that still looks like JSON. Common use cases include:
- LLM structured output: Clean model responses before seeding Kane AI or other automated test authoring flows.
- API and log fixtures: Recover truncated responses for regression cases tracked in Test Manager.
- Hand-edited configs: Fix quote style and trailing commas after quick edits in a text editor.
- Compact downstream payloads: After repair, send valid JSON through the JSON Minify tool when you need a single-line fixture.
- Structure inspection: Pipe repaired output into the JSON Parser when you need another view of nested values.
Frequently Asked Questions (FAQs)
Can JSON repair fix any broken JSON?
No. JSON repair fixes common syntax mistakes such as trailing commas, quote style, unquoted keys, comments, and truncated braces. It cannot invent missing field values or correct wrong data types. Always review repaired output before you trust it in production fixtures.
Does this JSON repair tool upload my data?
No. All processing happens in your browser. No data is uploaded to TestMu AI servers for the repair step itself. You can paste secrets or API payloads without sending them through a remote repair API, which keeps sensitive fixtures on the local page.
Can it repair JSON from LLM or ChatGPT output?
Yes. Language models often wrap JSON in markdown fences, add trailing commas, or emit Python True, False, and None. This tool strips fences, normalizes literals, and closes truncated braces so the result can pass JSON.parse when you build automated test fixtures.
What happens to trailing commas in JSON?
Trailing commas after the last property or array item are removed during repair. JavaScript object literals allow them, but RFC 8259 JSON does not. After repair, the document should parse with a strict JSON parser such as JSON.parse in the browser.
Does repair replace JSON validation?
No. Repair rewrites almost-JSON into parseable JSON. Validation checks that a document already conforms to the grammar. After repair, use the JSON Validator or JSON Prettify tools on TestMu AI to confirm structure and readability before you ship any fixture.
Can it fix truncated JSON missing closing braces?
Often yes. When a stream or LLM response cuts off mid-object or mid-array, the repairer closes open braces and brackets to produce the most complete valid document it can. Severely corrupted values may still fail and need a manual edit.
Does it convert Python True, False, and None to JSON?
Yes. Python-style True, False, and None become JSON true, false, and null during repair. That helps when you paste repr-style output or mixed Python and JSON logs into the input box before later validation, pretty-printing, download, or fixture reuse steps.
Is the repaired JSON always pretty-printed?
Yes in this widget. After a successful repair, the tool parses the fixed string and formats it with two-space indentation so you can review keys and nesting before copy or download. Use JSON Minify later if you need one compact line.
Why did Load from URL fail?
Some hosts block browser requests with CORS headers, so the fetch never returns the file body. If Submit fails, download the file yourself and use Upload instead. Only http or https URLs are accepted in the URL dialog on this page.
Can I repair a large JSON file at once?
Yes for typical fixture sizes under a few hundred kilobytes. Paste text, upload a .json or .txt file, or load from a URL. Auto Update debounces while you type so large pastes stay responsive in modern desktop browsers during repair.
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