JSON formatter & validator

Paste JSON on the left. Get pretty-printed output and validation on the right. Runs entirely in your browser.

What this does

It parses your JSON with the browser's native JSON.parse, then re-emits it formatted. If parsing fails, you get the exact error message with position information so you can find the bad comma or unclosed bracket.

Common JSON mistakes

Trailing commas — {"a":1,} is invalid JSON. (JavaScript allows it; JSON doesn't.)
Single quotes — 'key' is invalid. JSON requires "double quotes".
Unquoted keys — {key:1} is invalid. Keys must be quoted strings.
Comments — // like this are not allowed in standard JSON.
NaN / Infinity / undefined — not valid JSON values.

JSON spec quick reference

JSON values can be: a string (in double quotes), a number, true, false, null, an array [...], or an object {...}. Strings escape with backslash: \", \\, \n, \t, \uXXXX.