JSON Validator Developer
Check JSON for errors and get the exact line and column of the problem.
JSON Validator is a free online tool that check JSON for errors and get the exact line and column of the problem. It runs entirely in your web browser using plain JavaScript, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Developer
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- plain JavaScript
- Settings
- None — it just works
- Works offline
- Yes, after the first visit
About JSON Validator
Invalid JSON is almost always one of four things, and this reports which and where: a trailing comma after the last element, single quotes instead of double, an unquoted key, or a comment. All four are legal JavaScript and none is legal JSON — the format is a strict subset defined by RFC 8259, which is exactly the trap for anyone hand-editing a config file.
How to use it
- Paste the text you want to run through json validator.
- There is nothing to configure — the result updates as you type.
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
Questions
Why can JSON not have comments?
Douglas Crockford removed them deliberately, having seen comments abused to carry parsing directives. The practical workaround is a `_comment` key, or a format like JSON5 or JSONC where your tooling supports it.
Are trailing commas ever allowed?
Not in standard JSON. JavaScript, JSON5 and JSONC permit them, which is why they slip in so often — the file looks fine in an editor and fails at the parser.