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JSON Formatter
JSON Formatter & Validator — Free Online Tool
Paste JSON to format, validate, or minify — syntax errors report the exact line, entirely in your browser.
About JSON Formatter
Working with JSON data from an API response, configuration file, or database export? Unformatted JSON is nearly impossible to read, especially when deeply nested. This tool formats messy JSON into readable, properly indented output, making it easy to scan and understand the structure of your data. The rewrite moves whitespace only — every string, number, and keyword is copied byte for byte, so a 64-bit id or a trailing zero survives exactly as you pasted it instead of being rounded through a double. It validates your JSON in real time and shows clear, descriptive error messages for invalid input, and where the browser's parser reports a position the output pane becomes the failure report: the exact line and column, plus three lines of context with the offending character marked. Toggle between formatted and minified views with one click, which is useful when you need compact JSON for API requests or configuration files. Common use cases include debugging API responses, formatting configuration files for readability, validating JSON payloads before sending them, and minifying JSON to reduce payload size.
Questions
Is my JSON data sent to a server?
No. All formatting happens in your browser using JSON.parse and JSON.stringify. No data leaves your device.
What's the difference between Format and Minify?
Format adds indentation and line breaks for readability. Minify removes all whitespace to produce the smallest possible output — useful for APIs and configuration files.
Can it handle large JSON files?
It works well for JSON up to a few megabytes. Very large files may cause the browser tab to slow down due to rendering the formatted output.
Will formatting change my numbers or precision?
No. Format and Minify rewrite only the whitespace — every string, number, and keyword is copied byte for byte, so a 19-digit database id, a trailing .0, or 1e2 comes out exactly as you pasted it instead of being rounded through a floating-point double.
How do I find the syntax error in my JSON?
Paste the JSON and the output pane becomes the failure report: the parser's own message, the line and column where it stopped (when your browser's parser reports a position), and a three-line excerpt with the offending character highlighted. Everything before that character parsed fine, so the mistake is at or just before the mark.
Is my file uploaded to a server?
No. Transmute processes everything locally in your browser using JavaScript and WebAssembly. Your files never leave your device — there is no server, no upload, no cloud processing.