Loona JSON Formatter & Validator - Pretty Print and Minify JSON
Broken JSON is the most common five-minute delay in a developer's day - one missing comma and the whole payload fails. Paste your JSON below: if it is valid you get clean, readable output; if it is not, you get the precise position of the error instead of a useless "parse failed".
How to use the JSON Formatter
- Paste or type your JSON into the top box.
- Choose an indent style - 2 spaces, 4 spaces or tab.
- Click Format / Validate for readable output, or Minify for the smallest valid form.
- Copy the result or download it as a .json file.
How it works
The tool uses your browser's built-in JSON parser - the same strict parser your own JavaScript code uses - so a green light here means your JSON really is valid. Pretty-printing re-serialises the parsed value with your chosen indentation; key order is preserved exactly as written. Minifying removes every unnecessary space and newline without changing a single value. When parsing fails, the tool converts the parser's character position into a line and column and shows you the offending line.
Worked example
You receive {"user":"ahmed","roles":["admin","editor"],"active":true} from an API. Formatted with 2 spaces it becomes a clean nine-line document you can actually read - and if you accidentally delete the comma after "ahmed", the tool reports the error at the exact line and column instead of leaving you to hunt for it.
Frequently Asked Questions
Is this JSON formatter free?
Yes - completely free, with no sign-up, no size limit and no daily cap.
What happens when my JSON is invalid?
You get the parser's error message plus the exact line and column where parsing failed, and the text of that line, so you can fix it in seconds.
Does formatting change my data?
No. Formatting changes whitespace only. Minifying removes whitespace only. Keys, values and their order are untouched.
Is my JSON uploaded to a server?
No. Parsing and formatting happen 100% in your browser. API payloads and config files never leave your device.
Can I format really large JSON?
Yes - the practical limit is your device's memory. Files of several megabytes format in well under a second on a typical laptop.