Free Online JSON Formatter & Validator

Why use JSON Formatter & Validator

• Catches syntax errors that are invisible in a plain text editor -- trailing commas, unquoted keys, mismatched brackets.
• Switch between 2-space, 4-space, and tab indentation to match any project's conventions.
• Minify mode collapses JSON to a single line for API payloads, env vars, and config files.
• Syntax highlighting color-codes strings, numbers, booleans, and null so you can scan nested structures at a glance.

How it works

The formatter uses the browser's built-in JSON.parse() to validate your input against the JSON specification (RFC 8259). If parsing succeeds, the tool re-serializes the object with JSON.stringify() using your chosen indentation level, producing clean, consistently-formatted output. If parsing fails, the error message from the JavaScript engine identifies the character position where the syntax broke, which the tool surfaces as a human-readable error. Syntax highlighting is applied after formatting by scanning the output for token types -- string literals (in quotes), numbers, booleans (true/false), and null -- and wrapping each in a styled span. Minification re-serializes with no indentation or whitespace.

About this tool

Someone just sent you a 400-line JSON blob with no whitespace. Paste it here. You'll get indented, syntax-highlighted output in under a second. The validator catches the stuff that's invisible in a text editor -- trailing commas, unquoted keys, mismatched brackets -- and tells you the exact line and character position so you're not scanning hundreds of lines by hand. Switch between 2-space and 4-space indentation to match your project's conventions, or hit Minify to collapse everything to a single line for API payloads and environment variables. Syntax highlighting color-codes strings, numbers, booleans, and null, which makes it easy to scan deeply nested structures that would be a wall of text in VS Code's raw output panel. The minify mode is what you want when you need JSON inside an env var on Vercel (64 KB limit) or a URL parameter where whitespace isn't allowed. Error messages come straight from the JavaScript engine's JSON.parse(), so what you see here is the same error your code would throw at runtime. That saves a round trip.

How to use JSON Formatter & Validator

1. Drop in your JSON. Paste raw, minified, or partially-formatted JSON into the left panel. Validation fires immediately and flags the first syntax error it finds.
2. Check for errors. If something's off, an error banner shows the exact issue -- 'Unexpected token at position 142' or 'Trailing comma after last property'. Fix it and the error clears.
3. Pick your indent style. Select 2-space, 4-space, or tab indentation to match your project. The formatted output updates in real time.
4. Format or minify. Format gives you readable, indented JSON. Minify collapses it to a single line for API payloads and config files.
5. Copy the result. Click Copy to put the output on your clipboard. Paste it into your editor, Postman, or a CI config.

Use cases

• Your API just returned a 500 and the response body is a wall of unformatted JSON. Paste it here, find the nested error field in seconds.
• You're embedding a config object in a Vercel environment variable and need it on a single line under 64 KB. Hit Minify.
• You've got a webhook payload from Stripe that needs to go into a test fixture file. Format it, scan the structure, confirm it matches the docs.