What does the Diff tab show?

The Diff tab shows a line-by-line comparison of your original pasted JSON against the repaired output — red lines were removed or changed, green lines are the corrected versions. It tells you exactly what JSONBlitz fixed and why, so you can understand and fix the source rather than just copying the output.

Why is seeing the diff important?

Most JSON repair tools silently fix your data with no explanation. If you don't know what changed, you can't fix the source — your API, config file, or code — that produced the broken JSON in the first place. The diff is the audit trail.

Can I use the diff to improve my prompts or code?

Yes. If the diff shows trailing commas, your code or LLM prompt is generating them — fix it there. If it shows Python booleans, your serialisation step isn't converting them. The diff tells you exactly where to look.

Is my JSON private when using the diff feature?

Yes. All processing including the diff computation happens locally in your browser. Nothing is transmitted anywhere.

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JSONBlitz 100% PRIVATE

Input — paste anything

JSON Repair with Diff — See Every Change, Not Just the Output

Most JSON repair tools silently fix your data. JSONBlitz shows you a line-by-line diff of every change — what was removed, what was added, and why. Paste your broken JSON below, then click the ⚖ Diff tab to see the full repair audit trail.

Ready — paste JSON or any text containing JSON

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Tree view appears here after processing

Click nodes to copy JSONPath • Single-click a leaf to copy value

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Process JSON to generate code...

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Shows what JSONBlitz changed to fix your JSON. Process some broken JSON first.

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JSONBlitz — Fix Invalid JSON Instantly. Free Online JSON Formatter & Validator 2026.

JSONBlitz is a free, 100% private, client-side JSON formatter, validator, and repair tool. Paste messy JSON, console logs, API responses, or stack traces — JSONBlitz finds the JSON, fixes it automatically, and gives you clean output plus TypeScript interfaces, Zod schemas, and Python TypedDict code. Nothing ever leaves your browser.

How to Fix Invalid JSON Online Free

Paste any broken JSON into JSONBlitz. Common errors like trailing commas, single quotes instead of double quotes, unquoted keys, and JavaScript comments are all fixed automatically in one click. The status bar shows exactly what was repaired.

Fix Trailing Comma JSON Error

Trailing commas in JSON objects and arrays are one of the most common errors when copying JSON from JavaScript code. JSONBlitz removes trailing commas automatically and shows you what changed in the Before/After tab.

Extract JSON from Console Logs and Error Messages

Paste a full console log, stack trace, terminal output, or Slack message that contains JSON. JSONBlitz automatically detects and extracts the JSON portion, even if it is buried in surrounding text. Works with ChatGPT and Claude AI output too.

Free TypeScript Interface Generator from JSON

Paste any JSON and click the TS+Zod tab to instantly generate recursive TypeScript interfaces, Zod validation schemas, and Python TypedDict classes. No signup required. Works completely offline.

100% Private JSON Tool — Safe for API Keys and Production Data

JSONBlitz processes everything locally in your browser — your JSON never leaves your device. No data is transmitted anywhere. Safe for API keys, authentication tokens, credentials, and sensitive production data.

Frequently Asked Questions

What causes trailing commas in JSON?: Trailing commas are valid in JavaScript and many other languages, so developers naturally write them out of habit. Copying a JS object literal directly into a JSON context brings the trailing comma with it. JSON spec (RFC 8259) explicitly forbids them.
Where exactly does a trailing comma break JSON?: After the last item in an array or the last key-value pair in an object. [1, 2, 3,] and {"a":1,} are both invalid. JSONBlitz removes these automatically.
Can JSONBlitz fix trailing commas in nested objects?: Yes. The fix engine handles trailing commas at any depth — inside nested objects, nested arrays, and mixed structures. All are repaired in a single pass.
Does JSONBlitz fix other errors at the same time?: Yes. Single quotes, unquoted keys, JavaScript comments, and smart quotes are all fixed in the same pass as trailing commas.