JSON Formatter & Beautifier
Format, beautify, and validate JSON instantly in your browser. Your data never leaves your device.
Use this free JSON formatter to instantly beautify, validate, and minify JSON. Paste messy or minified JSON and get clean, readable output with proper indentation — or compress it back down to a single line. It is perfect for debugging API responses, config files, and log data.
How to use it
No account, no upload — it all happens on your device.
When developers reach for a JSON formatter
Common workflows where pretty-printing or validating JSON saves time.
JSON is the lingua franca of modern APIs, config files, and browser storage. It is also famously unforgiving — one stray comma or unbalanced bracket invalidates the entire document. Engineers reach for a formatter dozens of times a week to:
- Inspect an API response. Servers minify JSON to save bytes, which makes it nearly impossible to read in a browser tab. Pasting the body into a beautifier reveals the structure instantly.
- Diff two configs. Reformatting both files to the same indentation makes a line-by-line diff meaningful instead of a wall of whitespace noise.
- Validate a hand-edited file. If your application throws
SyntaxError: Unexpected token, the formatter highlights the exact position so you can find the trailing comma or missing quote. - Shrink JSON for transport. The Minify mode strips every byte of whitespace, which can cut payload sizes by 20–40% before gzip.
Worked examples
How input becomes output in each mode.
| Mode | Input | Output |
|---|---|---|
| Beautify (2-space) | {"name":"Ada","skills":["math","code"]} | { "name": "Ada", "skills": ["math", "code"] } |
| Minify | { "id": 1, "active": true } | {"id":1,"active":true} |
| Validation error | {"a": 1,} | Unexpected token } in JSON at position 8 |
Common JSON mistakes
Mistakes that look like bugs in your code but are really invalid JSON.
- Trailing commas. JSON does not allow them, even though JavaScript does.
{ "a": 1, }is invalid; remove the last comma. - Single quotes. JSON strings must use double quotes.
{ 'name': 'Ada' }fails to parse. - Comments. JSON has no comment syntax — neither
//nor/* */. If you need comments, look at JSON5 or JSONC. - Undefined or functions. JSON only encodes strings, numbers, booleans, null, arrays, and objects.
undefinedand functions cannot be serialized. - NaN and Infinity. Not valid JSON numbers. Convert them to
nullor a string before serializing.
Performance and limits
The formatter uses your browser's native JSON.parse and JSON.stringify — the same code that powers fetch() response decoding. That means it can handle multi-megabyte payloads without breaking a sweat. Two practical limits to keep in mind:
- Very deeply nested structures (~10,000+ levels) can blow the call stack. If you hit one, flatten the structure before formatting.
- Browsers cap text input at a few hundred megabytes. For files larger than that, stream the JSON through a CLI tool like
jqorjson_ppinstead.