JSON & Data/JSON Formatter & Validator
JSON Formatter & Validator
Paste or upload JSON, get it pretty-printed and checked for syntax errors. Nothing leaves your browser.
What this does
JSON that comes back from an API or a log file is usually minified — all on one line, no spacing. That's efficient for machines and unreadable for people. This tool parses the JSON, checks that it's syntactically valid, and re-prints it with consistent indentation so you can actually read the structure. If the JSON is broken — a missing comma, an unescaped quote, a trailing comma — it tells you the line and column where parsing failed instead of just saying "invalid."
Common causes of invalid JSON: trailing commas after the last item in an array or object, single quotes instead of double quotes, unquoted object keys, and JavaScript-only values like undefined or comments, none of which are valid in strict JSON.
FAQ
Is my data uploaded anywhere?
No. Whether you paste text or upload a file, everything is read and parsed locally using your browser's built-in JSON engine. Nothing is sent to a server, logged, or stored.
Is there a size limit?
File uploads are capped at 5MB to keep the UI responsive, since formatting happens on your device's CPU rather than a server. Pasted text has no hard limit, but very large payloads may feel slow.
Why does it reject JSON that works in JavaScript?
JSON is stricter than a JavaScript object literal. Trailing commas, single-quoted strings, and unquoted keys are all valid JS but invalid JSON — the validator follows the JSON specification, not JavaScript's more permissive syntax.
Need to explore a large payload instead of just formatting it? Try the JSON Tree Viewer →