JSON Formatter & Validator
Paste messy JSON to beautify it with clean indentation, minify it to one line, or validate it with clear error messages — all in your browser.
Understanding the JSON Formatter & Validator
This tool takes raw or messy JSON and pretty-prints it with consistent indentation, or minifies it down to a single line. It also validates structure, flagging the exact line where a bracket, quote, or comma goes wrong. Developers, API users, and QA testers use it to read API responses, clean up config files, and confirm a payload is syntactically correct before sending it. Everything runs locally in your browser, so the data you paste never leaves your device.
How it works
The tool parses your input with the browser's native JSON.parse engine. If parsing succeeds, the data is re-serialized with JSON.stringify using a chosen indent (2 or 4 spaces, or tabs) to beautify, or with no spacing to minify. Validation comes free: when JSON.parse throws a SyntaxError, the message and position are surfaced so you can jump to the problem. Because parsing and formatting happen entirely in JavaScript on your machine, nothing is uploaded. Read the result as a tree of objects, arrays, strings, numbers, booleans, and null, with nesting shown by indent depth.
Worked example
Paste {"name":"Ada","langs":["py","js"],"active":true}. With 2-space indent the formatter returns a stacked, readable block: name on one line, the langs array with each value indented, and active at the bottom. Switch to minify and the same object collapses back to 54 characters on one line, ideal for embedding in a URL or a curl command. Now delete the closing brace and revalidate: the tool reports "Unexpected end of JSON input", telling you a bracket is missing.
Tips & common mistakes
- A trailing comma after the last array or object item is invalid JSON, even though JavaScript allows it; remove it.
- Keys and string values must use double quotes, not single quotes, or parsing fails.
- Minify before pasting JSON into query strings or logs to save space; beautify when debugging.
- JSON has no comments; strip // and /* */ before validating or use JSON5 elsewhere.
- If validation fails, read the reported position first, then check the character just before it.
Related tools
Frequently Asked Questions
Does this validate my JSON?
Yes. If your JSON is invalid, the tool shows the exact parser error message so you can find and fix the problem.
What does minify do?
Minify removes all whitespace and line breaks to produce the smallest valid JSON — useful for APIs and saving bandwidth.
Is my data sent anywhere?
No. All formatting and validation happen locally in your browser. Your JSON is never uploaded.