JSON Formatter

How to format JSON

1. Paste your JSON into the input area, minified, pretty-printed, or anything in between.
2. The formatter validates and pretty-prints your JSON automatically.
3. Adjust the indent size (2 or 4 spaces) if needed.
4. Click "Copy" to copy the formatted JSON to your clipboard.

Common uses

• Pretty-printing API responses to make them readable during debugging, also useful alongside JWT decoder when inspecting auth tokens
• Minifying JSON before including it in source code or config files
• Validating JSON structure before sending to an API or database, convert spreadsheet data first with CSV to JSON

Technical specification

• Algorithm or formula: JSON.parse to verify and structure, then JSON.stringify with a numeric indent argument (2 or 4) for pretty mode. Sort-keys mode recursively sorts object keys alphabetically before stringifying; keys that are whole numbers come first, in numeric order. Minify mode stringifies with no indent.
• Browser API or library: Native JSON.parse and JSON.stringify. Where the browser supports JSON.parse source text access, numbers keep the exact text you typed. No external library.
• Input limits: Bounded by browser memory. Multi-megabyte JSON formats quickly on modern devices.
• Output: Formatted, minified, or sorted JSON text. Parse errors include the line and column when the engine reports a position.
• Known limitations: Strict JSON only; comments, trailing commas, and other JSON5/JSONC extensions are flagged as invalid. Order of original object keys is not preserved when sorting. If a key appears more than once in an object, only the last value is kept, and keys that are whole numbers are listed first. In browsers without source text access, integers longer than 15 digits may be rounded and a note says so.

Frequently asked questions

What is the largest JSON file this tool can format?

Roughly 10 MB before the browser tab starts to slow down. The formatter uses the browser's native JSON.parse and JSON.stringify, so the practical limit is your device's available memory. All processing runs in your browser.

Does my JSON get sent to a server?

All formatting and validation happens in your browser using JavaScript. Our servers are not involved at any point.

What happens if my JSON is invalid?

The tool shows an error message, with the line and column of the problem when the browser reports them, so you can fix it quickly.

Can I format JSON with comments?

Standard JSON does not allow comments. If your input contains them (JSONC format), the tool will flag them as invalid. Remove comments before formatting.

Does the formatter keep large numbers exact?

In browsers that support JSON.parse source text access, numbers keep the exact text you typed, including integers longer than 15 digits and values such as 1.0. In other browsers those integers may be rounded, and a note under the output says so.