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📐 JSON Formatter
Paste your JSON. Get it back pretty-printed, with errors flagged by line number. That's it. No signup, no API call, no upload — the parser lives in your browser, and so does your data. Useful when an API blasts a single ugly line at you, or when a config file refuses to load and you need to find the rogue comma.
Examples
{"name":"Alice","tags":["admin","beta"],"active":true}{
"name": "Alice",
"tags": [
"admin",
"beta"
],
"active": true
}{"a": 1, "b": 2,}Unexpected token } at position 16Trailing commas are not valid in JSON (unlike JS).
{
"id": 1,
"value": "x"
}{"id":1,"value":"x"}Frequently asked questions
Is my JSON sent to a server?
No. Open the Network tab in DevTools and watch — there are no outgoing requests when you paste. Everything happens via the browser's built-in JSON.parse and JSON.stringify. If you don't trust me, view source.
Does it validate against a JSON Schema?
No — this tool only checks that the JSON is syntactically valid. For schema validation use a library like Ajv or a dedicated tool.
How big a JSON can it handle?
Anything your browser can hold in memory. We have tested files up to ~100 MB without issue on a modern laptop. Very large files may freeze the UI for a few seconds during parsing.
Why does it complain about my JSON when JavaScript accepts it?
JSON looks like JS object literals but is much stricter. The four things that bite you: keys must be double-quoted (not single), no trailing commas, no comments anywhere, no single-quoted strings. JS5/JSONC relax those rules but real JSON does not.
Can I use this in production?
Yes, it is free for any use (personal or commercial). But for programmatic JSON work, use the native JSON.parse / JSON.stringify in your code directly.
About this tool
JSON Formatter runs entirely in your browser using standard Web APIs. No data is sent to any server. The source for this tool is in our public GitHub repository.
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Why this tool
vs typical free web-tool sites
| 1vw | Typical free site | |
|---|---|---|
| Price | Free | Free |
| Signup required | No | Often (for premium features) |
| Ads inside the tool | No | Yes (banner + video) |
| Data sent to server | No (browser-only) | Yes (inputs analyzed for ads) |
| Total tools | 96 | Often <20 or scattered across sites |
| Bookmarkable URL per tool | Yes | Mixed |
| Loads in under 1s | Yes (static) | Often slow (ad tracking) |
| Multilingual | EN / ES / PT / FR / DE | Usually EN only |
| Open source | Yes | No |