JSON Validator

Paste JSON to find out whether it follows the standard exactly (RFC 8259 and ECMA-404). If it does not, the validator stops at the first problem and shows the line, the column, the offending snippet with a caret under it, and what to change. If it does, you see the top-level type, nesting depth, number of keys and array items, and the size in bytes, plus warnings for duplicate keys and integers JavaScript cannot hold exactly.

How to use this tool

1. Paste the JSON — an API response, a config file or a log line.
2. Read the verdict: Valid JSON or Invalid JSON.
3. If invalid, go to the line and column shown, apply the suggested fix and watch the result update.
4. Optionally tick Treat duplicate keys as errors for a stricter check.

Formula

JSON text = whitespace, one value, whitespace

Whitespace means only space, tab, line feed and carriage return. Strings need double quotes, numbers are plain decimals without leading zeros, and the literals true, false and null are lowercase. Comments, trailing commas, NaN and undefined are not part of JSON.

Example

{"a":1,} is invalid: the validator reports line 1, column 7 — the comma — because JSON does not allow a comma before }. Removing it gives {"a":1}, which is valid: an object with 1 key, nesting depth 1 and a size of 7 bytes.