JSON Validator
Check whether JSON is valid, locate the error, and find repeated keys that parsers silently discard.
Your result will appear here as soon as you add some input.
How to use it
- 1Paste your document into the input box, or type it directly.
- 2Adjust the options if you need something other than the defaults.
- 3The result updates as you type.
- 4Copy the result to your clipboard or download it as a file.
About the JSON Validator
Errors are reported with a line and column and an explanation of the most likely cause. The four that account for most invalid JSON are a trailing comma, single quotes, an unescaped newline inside a string, and a missing closing bracket.
Valid documents are also scanned for keys repeated inside the same object. That is legal JSON but data-losing: parsers keep only one value and none of them warn you, so a duplicate key can silently discard data for years.
Structure is reported too - object and array counts, nesting depth and total keys - which is often enough to spot that a payload is not shaped the way the API documentation claims.
Questions people ask
Is your document uploaded to a server?
No. This tool runs entirely in your browser using standard web APIs, so your document never leaves your device. You can confirm it by opening your browser's network panel while the tool runs, or by disconnecting from the internet after the page has loaded.
Is it free, and do I need an account?
Yes, it is free, and there is no account, no sign-up and no watermark on the result. The project is funded by optional donations.