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JSON formatter, validator & minifier
Validate, beautify and minify JSON entirely in your browser, with instant error checking down to the line and column.
This tool runs entirely on your device using the browser's native JSON.parse and JSON.stringify. No data is sent to a server, and it keeps working offline once the page has loaded.
What this JSON formatter does
Paste or type JSON on the left and the tool checks it as you go. Valid input is confirmed with its top-level type, key or item count and byte size; invalid input is flagged with the parser's message and the line and column where it failed. Press Beautify to pretty-print with your chosen indentation, or Minify to collapse everything onto a single line. The result appears on the right, ready to copy or download as a .json file. Nothing ever leaves your browser.
How to read and fix a JSON error
JSON is stricter than JavaScript. Keys and strings must use double quotes, trailing commas are not allowed, comments are forbidden, and every bracket and brace must be balanced. When parsing fails, the status line shows a message such as “Unexpected token” together with a line and column. Jump to that spot in the input. The mistake is usually right there or one token earlier. The most common fixes are removing a stray comma, swapping single quotes for double quotes, quoting a bare key, or closing an open array or object.
Beautify vs minify: which to use
Use Beautify while you are reading, diffing or debugging. Indentation makes the structure obvious and pairs well with version control. The 2-space setting matches most style guides; 4 spaces or tabs suit teams that prefer them. Use Minify for anything that travels or is stored at scale: API responses, configuration bundled into a build, or documents saved to a database. Minified JSON can be a fraction of the beautified size, which adds up across millions of requests. Switch between the two at any time without touching the original.
Everything runs in your browser
This formatter calls the browser's built-in JSON.parse and JSON.stringify, so there is no server, no upload and no network request. That keeps sensitive payloads (tokens, personal data, internal API responses) on your own machine, and it means the tool works offline once loaded. Because parsing is native, it is fast: the same engine your applications rely on does the work here, then hands you Copy and Download so the result never needs to touch a third party.
Frequently asked questions
Does this JSON formatter send my data to a server?
No. Everything runs locally in your browser using the built-in JSON parser. Your JSON is never uploaded, logged or transmitted. You can disconnect from the internet and the tool keeps working.
Why do I get an “Unexpected token” error?
That message means the parser reached a character it did not expect. The usual causes are a trailing comma before a closing bracket, single quotes instead of double quotes, unquoted object keys, or a missing bracket. The line and column point to where parsing gave up, which is usually just after the real mistake.
What is the difference between beautify and minify?
Beautify re-indents the JSON with line breaks so a human can read it. Minify strips every optional space and newline to make the smallest possible payload for storage or network transfer. Both describe exactly the same data. Only the whitespace differs.
Does formatting ever change my data?
It re-serialises the parsed value, so the data stays the same but a few normalisations apply: duplicate keys collapse to the last one, numbers are rewritten in canonical form (1e3 becomes 1000), and non-significant whitespace is rebuilt. Object key order is otherwise preserved as written.
Can it handle large JSON files?
Yes, up to whatever your browser's memory allows. Files of a few megabytes format almost instantly; very large inputs may freeze the tab for a moment while the native parser works, since everything happens on the page with no server to offload to.