TabBench
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JSON Formatter & Validator

A client-side developer utility to format unreadable JSON, detect syntax mistakes with exact line diagnostics, minify data, and inspect structures securely without data leaves your browser.

Payload Size: 215 bytes
Root Properties: 6

Unformatted JSON is hard to scan and harder to debug — a single missing comma in a 2,000-line API response can cost you an afternoon. This formatter parses your JSON with the browser's native engine, reports the exact line and column of any syntax error, and re-indents the result so nested structures become obvious at a glance. Nothing is uploaded: the parse happens in your tab, which matters when the payload contains tokens, customer records, or anything else you would not paste into a random website.

How to format JSON online

  1. Paste your raw JSON into the input box, or drop a .json file onto it.
  2. Choose your indentation — 2 spaces, 4 spaces, or tabs — to match your project's style guide.
  3. Click Format. Valid JSON is re-indented instantly; invalid JSON stops at the first error with a line number.
  4. Fix any reported syntax error and re-run. The most common causes are trailing commas and single quotes instead of double quotes.
  5. Use Minify to strip all whitespace when you need the smallest possible payload, then copy the result.

The JSON Formatter & Validator runs entirely in your browser — nothing you enter is uploaded, stored, or logged.

When to use this tool

Debugging API responses

When an endpoint returns a wall of unbroken text, formatting it is the fastest way to confirm the shape of the response — whether a field is nested one level deeper than you expected, or whether an array came back empty rather than absent.

Validating config files before deploy

A malformed package.json, tsconfig.json, or CI config will fail your build minutes after you push. Validating locally first turns a failed pipeline into a five-second check.

Shrinking payloads for production

Minified JSON removes every byte of indentation and newline. On large embedded configuration blobs this routinely cuts 20–30% of the transfer size with no change in meaning.

Things worth knowing

  • JSON requires double quotes around keys and string values — single quotes are a syntax error, even though JavaScript accepts them.
  • Trailing commas after the final element of an array or object are invalid JSON, though most linters allow them in JavaScript source.
  • JSON has no comment syntax. If your file has // or /* */ comments, it is JSON5 or JSONC, not JSON.
  • NaN and Infinity are not valid JSON values; they must be encoded as strings or null.

Frequently Asked Questions

Is my JSON stored?

No. Everything runs purely in your local browser JavaScript memory.

What is the difference between formatting and validating JSON?

Validating checks whether the text is legal JSON and reports errors. Formatting re-indents already-valid JSON for readability. This tool does both in one pass: it must parse successfully before it can re-print, so a successful format is also proof of validity.

Why does my JSON fail with 'Unexpected token' errors?

In order of frequency: a trailing comma before a closing bracket, single quotes instead of double quotes, an unescaped newline or quote inside a string, or an unquoted object key. The reported line number points at where the parser gave up, which is usually one character after the real mistake.

Is there a size limit on the JSON I can format?

The practical limit is your device's available memory, since the whole document is parsed in the tab. Files up to a few megabytes format essentially instantly; very large documents in the tens of megabytes may briefly freeze the tab while parsing.

Does formatting change my data?

No. Formatting changes only whitespace. Key order is preserved, and values are re-serialized exactly as parsed. The one thing to be aware of is that JSON numbers beyond JavaScript's safe integer range lose precision on any round-trip, which is a property of JSON itself rather than this tool.

Can I use this for JSON Lines or NDJSON?

Not directly — those formats put one independent JSON document per line, which is not a single valid JSON document. Format each line separately, or wrap the lines in an array first.

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