About the JSON Validator
This validator uses a hand-written strict parser instead of relying on the browser's JSON.parse message, so every browser reports the same precise position. The result box quotes the offending line with a caret (^) under the character where parsing stopped, and explains the likely cause — for example Missing comma between properties or Property names must be wrapped in double quotes.
It also reports problems that are technically valid JSON but cause real bugs. Duplicate keys: RFC 8259 says names should be unique, and when they are not, behaviour differs between parsers — JSON.parse and Python keep the last value, some streaming parsers keep the first, and security tools may see a different value than your application. Each duplicate is listed with its path (for example $.billing.currency) and both line numbers. Unsafe integers above 253 − 1 are flagged because JavaScript rounds them.
Validation checks syntax only. To check that fields have the right types or required properties you need a JSON Schema validator. The document never leaves your browser, so it is safe to paste configuration files or API payloads that contain internal data.
How to use it
- Paste your JSON or open a file.
- Read the result above the editors: green means valid.
- If invalid, go to the reported line and column; the caret marks the character.
- Review any duplicate-key warnings and rename or remove them.
Frequently asked questions
Are duplicate keys allowed in JSON?
Why is the error column after the real mistake?
Is a single string or number valid JSON?
"text", 42 or null — is a valid top-level document. Some older APIs still expect an object or array.