UlvixorJSON Formatter & Validator
Paste your JSON and get an instantly formatted, readable version, with line-by-line syntax error detection. All processing happens right in your browser.
How it works
- Paste or type your JSON into the input panel.
- The formatter validates the syntax and shows the indented result in real time.
- If there's an error, you'll see the exact message so you can fix it.
- Copy the result or download it as a .json file.
Use cases
- Debug API responses that are hard to read crammed onto a single line.
- Validate that a JSON config file has no syntax errors.
- Minify JSON before shipping it to production to reduce its size.
- Review and share webhook payloads in a readable format.
Use cases
- Debug API responses that are hard to read crammed onto a single line.
- Validate that a JSON config file has no syntax errors.
- Minify JSON before shipping it to production to reduce its size.
- Review and share webhook payloads in a readable format.
Common mistakes
- Using single quotes instead of double quotes for keys or strings.JSON requires double quotes ("). The validator points to the exact line and column where it found the unexpected character.
- Leaving a trailing comma after the last element of an array or object.Unlike JavaScript, JSON doesn't allow trailing commas. Remove the comma before the closing } or ].
- Writing comments inside the JSON.JSON doesn't support comments (// or /* */). If you need to document the file, use a dedicated field like "_comment".
Frequently asked questions
No. All formatting and validation happen locally in your browser using JavaScript. Your JSON never leaves your device.
The tool shows a specific error message indicating exactly which part of the JSON is invalid, so you can fix it quickly.
Yes, your browser can handle JSON files several megabytes in size without trouble. For extremely large files, performance depends on your device.
Formatting adds indentation and line breaks to make JSON readable. Minifying strips out all unnecessary whitespace to reduce file size.
Alternatives
From the terminal, tools like jq or python -m json.tool give a similar result without leaving the command line, and most code editors format JSON with a built-in shortcut. This tool's advantage is not depending on installing anything, and being able to share the result with anyone instantly.