Website Tools

JSON Validator

Instantly check whether your JSON is valid, right in your browser.

Free & instant No signup How to use FAQ

Paste your JSON

Not sure what to enter?

Paste your JSON below to instantly check whether it's valid - entirely in your browser, nothing is sent to our servers.

How do I check if JSON is valid?

Paste the JSON into the box above and click Validate JSON. The validator parses it exactly as a program would and either confirms it is valid or shows the error - common causes are trailing commas, single quotes instead of double quotes and unquoted keys. It runs entirely in your browser.

How to validate JSON

Paste the JSON into the box above.
Click Validate JSON.
If it is invalid, go to the reported position and fix the problem.
Remember JSON requires double-quoted keys and strings and allows no trailing commas or comments.

Related checks

To pretty-print valid JSON, use the JSON Formatter.
To inspect a JSON Web Token, use the JWT Decoder.

JSON is stricter than the JavaScript it is based on: property names and strings must use double quotes, trailing commas and comments are not allowed, and values such as undefined or NaN are invalid. The validator checks your input against that strict standard and, when it fails, shows the browser parser's error message, which usually names the unexpected character and its position. Typical uses are checking an API response, a webhook payload or a configuration file such as package.json before relying on it. JustChecker builds tools that respect your data - this one never leaves your browser.

Frequently Asked Questions

No - this tool runs entirely in your browser using JavaScript. Your JSON is never transmitted anywhere.

It catches syntax errors like missing commas, unmatched brackets/braces, trailing commas, and improperly quoted keys or strings - anything that would make the JSON fail to parse.

Valid JSON only means the syntax is correct - it doesn't check whether the data itself matches what your application or API expects (that would require a schema validator).

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