Paste JSON to check it as you type. Every error points to its line and column with a plain explanation, and nothing you paste leaves your browser.
Check whether your JSON is valid, and find out exactly what is wrong when it is not. The validator checks every rule of standard JSON as you type and points to the line and column of the first error, with a message that says how to fix it - a trailing comma, a missing quote, a comment, an unclosed bracket.
No. Everything runs in your browser. Nothing you paste or upload is sent anywhere, logged or stored, so it is safe to use with API responses and config files.
Most online formatters convert your text to JavaScript numbers and back, which silently rounds anything beyond 2^53 - an ID like 12345678901234567890 becomes 12345678901234567000. This tool keeps every number, escape and key exactly as written and only changes the spacing.
Every rule of standard JSON: trailing commas, single quotes, comments, unquoted keys, missing commas or colons, mismatched brackets, unclosed strings, leading zeros, NaN and Infinity, and Python-style True, False or None. Each error shows the line, the column and a plain explanation.
Yes. A key that appears twice in the same object is valid JSON but usually a mistake, because most parsers keep only the last value. The tool lists each duplicate with its line number as a warning.
There is no upload limit, because nothing is uploaded. Very large documents of several megabytes still work; above about 200 KB the colours are switched off to keep typing fast.