Free JSON Validator Online
Paste your JSON below to instantly validate its syntax. Errors are pinpointed with exact line and column numbers. 100% browser-based — your data never leaves your device.
About the JSON Validator
This online JSON validator checks your JSON document against the RFC 8259 specification using the browser's native JSON.parse() engine. Any syntax error — such as a trailing comma, unquoted key, or mismatched bracket — is reported with the exact position so you can jump straight to the problem line.
Unlike a formatter that also reformats output, this validator is focused exclusively on correctness: it tells you whether your JSON is valid or exactly why it is not, making it ideal for CI/CD pipeline checks, API response debugging, and config file validation.
How to Validate JSON
Paste Your JSON
Copy your JSON string, file contents, or API response and paste it in the editor.
Click Validate
Press "Validate JSON". A green banner means valid; a red banner shows the first error.
Fix Errors
Use the reported line/column to navigate to the problem and correct it, then validate again.
Common JSON Errors
- Trailing comma —
{"a":1,}is invalid; remove the last comma - Single quotes — JSON requires double quotes for strings and keys
- Unquoted keys —
{name:"value"}is JavaScript, not JSON - Comments — JSON does not support // or /* */ comments
- Undefined / NaN / Infinity — these JS values are not valid JSON
- Missing comma between array elements or object members
Frequently Asked Questions
JSON (JavaScript Object Notation) is a strict data interchange format derived from JavaScript object syntax. Unlike JS objects, JSON requires double-quoted keys, does not allow trailing commas, comments, undefined, NaN, or function values.
Yes. The validator uses the browser's built-in parser which can handle files of several megabytes. The only limit is your device's available memory.
JSON.parse() stops at the first syntax error it encounters, because subsequent tokens may only be errors as a result of the earlier issue. Fix the first error and re-validate to uncover any remaining problems.
No. JSON5 is a superset of JSON that allows comments, trailing commas, and single-quoted strings. This validator checks standard JSON (RFC 8259). JSON5 will fail validation here unless it is also valid standard JSON.