How to use JSON Validator
- Paste the JSON you want to check.
- Read the result: a green summary for valid input or a red error pointing at the exact position.
- Apply the hint (for example remove a trailing comma) and re-validate.
JSON Validator features
- Strict RFC 8259 syntax validation using the native parser
- Line and column of the first error plus a plain-language hint and excerpt
- Duplicate-key detection with the names of the offending keys
- Warning for integers that lose precision in JavaScript
- Summary of root type, size, depth, keys and value distribution when valid
- Validates live while you edit
JSON Validator example
Catch a trailing comma
Input:
{
"items": [1, 2, 3],
"total": 3,
}Output:
Invalid JSON near line 4, column 1.
Trailing commas are not allowed before } or ].Frequently asked questions about JSON Validator
Which standard is used for validation?
RFC 8259 (the current JSON standard). The check uses the browser's native parser, so anything it accepts will also be accepted by every mainstream JSON library.
How precise is the error location?
The line and column point at the first character the parser could not accept. The hint explains the usual cause — trailing commas, single quotes, unquoted keys, comments or a missing bracket.
Does it detect duplicate keys?
Yes. Duplicate keys are technically allowed by the standard but almost always a bug, so the validator warns you and names the keys involved.
Can I validate JSON against a schema here?
This tool checks syntax only. Use the JSON Schema Validator to check structure, types and required fields.
Technical notes
The validator keeps the input in the browser and never sends it anywhere. Beyond syntax, it scans the raw text for duplicate keys per object scope (which JSON.parse silently collapses) and for integer literals beyond 2^53 − 1, both frequent sources of subtle production bugs.