Is my JSON sent to a server?

No. Parsing, formatting and validation all happen in your browser using the built-in JSON.parse and JSON.stringify. Nothing is uploaded.

How do I know if my JSON is valid?

If it's valid you'll see a green confirmation and the formatted output. If not, the exact parser error message is shown, usually with the character position so you can jump to the problem.

Can it handle large JSON?

Yes, within your browser's memory. Because it runs locally there are no upload-size limits, though very large files (tens of MB) may render slowly.

What is the difference between formatting and minifying JSON?

Formatting (pretty-printing) adds line breaks and indentation so the structure is readable. Minifying strips all whitespace down to a single line to make the payload as small as possible — useful for API responses and config embedded in code.

Why does my JSON fail with "Unexpected token"?

The most common causes are a trailing comma after the last item, single quotes instead of double quotes around keys/strings, unquoted keys, or a missing closing bracket. JSON requires double quotes and forbids trailing commas and comments.

Does this validate JSON or just format it?

Both. The tool runs JSON.parse first, so any output you see has been fully parsed and is guaranteed valid JSON. If parsing fails you get the error instead of output.

Can I change the indentation width?

Yes. You can set the indent to 2 spaces (the common default), 4 spaces, or other widths before pretty-printing.

JSON Formatter & Validator

Format and validate JSON in your browser

This tool pretty-prints, minifies, and validates JSON without sending it anywhere. Paste an API response, a config file, or a log line and get clean, indented JSON back — or a precise error message if it’s malformed. It’s built for developers debugging APIs, anyone tidying config files, and people who handle sensitive payloads they don’t want pasted into a random website.

How it works

The tool runs the browser’s native JSON.parse(input). If parsing succeeds, the result is re-serialised with JSON.stringify(parsed, null, indent) for pretty-printing (you choose the indent width, default 2 spaces) or JSON.stringify(parsed) with no spacing for minifying. Because it parses before re-printing, any formatted output is guaranteed to be valid JSON. If JSON.parse throws, the parser’s own error message — often including the character position — is shown so you can locate the problem.

Example

Paste this messy input:

{"name":"Ada","roles":["admin","editor"],"active":true}

Pretty-printing with a 2-space indent returns:

{
  "name": "Ada",
  "roles": [
    "admin",
    "editor"
  ],
  "active": true
}

Minifying the same data collapses it back to one line with no spaces.

Common JSON syntax errors

Error message	Likely cause
`Unexpected token } in JSON`	Trailing comma after the last item
`Unexpected token '`	Single quotes used instead of double quotes
`Expected property name`	An unquoted object key
`Unexpected end of JSON input`	A missing closing `}` or `]`
`Unexpected non-whitespace character`	Extra content after the JSON value

Everything runs locally in your browser — your JSON is never uploaded.