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JSON Validator

Check whether a document is valid JSON. When it is not, the line and column are shown along with the offending line and a caret under the character that broke the parse — which is the part most validators leave out.

Status

Waiting for input

Your JSON stays on your device

Parsing happens entirely in your browser. Nothing you paste is uploaded — worth knowing, since API responses often contain real customer data.

How to use this tool

  1. Paste the JSON you want to check.
  2. A valid document reports its structure: key count, nesting depth and the number of objects and arrays.
  3. An invalid one reports the line, column and the character that caused the failure.

Notes and limitations

  • This checks syntax, not meaning. Valid JSON can still be the wrong shape for your API — that requires a JSON Schema validator, which is a different job.
  • The structure summary is useful for spotting problems that are not syntax errors: an unexpectedly deep nesting level or a key count far from what you expected usually means the data is not what you think it is.
  • Duplicate keys are technically allowed by the specification and most parsers silently keep the last one. This tool follows the same behaviour, so a duplicate will not be flagged.
  • Everything runs in your browser and nothing is uploaded. That said, treat any third-party website with caution when handling production data — if a value would cause real damage if leaked, process it with your own local tooling instead.

Frequently asked questions

What makes JSON invalid?

Most often: single quotes, trailing commas, unquoted keys, comments, or an unescaped control character inside a string. The specification is deliberately strict, which is what makes it safe to parse anywhere.

Is a bare string or number valid JSON?

Yes. Since RFC 7159 any JSON value is a valid document, so "hello" and 42 both parse. Older parsers required an object or array at the top level.

Does this check my JSON against a schema?

No. It checks that the syntax is correct. Checking that the right fields are present with the right types needs JSON Schema and a schema to validate against.

Are duplicate keys an error?

Not formally. The specification says behaviour is undefined and virtually every parser keeps the last occurrence, so this tool accepts them too. They are still worth avoiding.

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