JSON Validator
Check JSON structure and configurations for errors offline in the browser.
🔒 Processed entirely in your browser — nothing you enter here is ever uploaded.
The result appears on this page after you run the tool. Nothing you enter is uploaded.
Result
About this tool
Are you familiar with the situation where you copy the JSON configuration, run the project, and everything breaks because of one missing comma or extra quotes, and you spend a lot of time searching?
With our tool, you will be able to check the JSON structure quickly and completely anonymously (the data is processed locally and does not leave your browser). We will easily highlight the wrong line, show the exact location of the problem and help you fix the structure in one click.
Just paste your text and we'll find the missing character and help you fix the format. Among the unusual features is the detection of duplicate keys, which are often ignored by other validators.
Example. The text {"a":1,"a":2} is flagged for a duplicate key even though JSON.parse would keep the last value.
Limit. A trailing comma is a syntax error, and comments are not allowed.
Is it safe to paste a real API response or config file with sensitive data?
Yes — validation happens entirely in your browser via the same JSON.parse engine used by browsers and JavaScript runtimes, and the text you paste is never sent anywhere. You can verify this yourself in your browser's developer tools: open the Network panel and paste your JSON; no request carrying it will appear.
Why does the error point to a line where everything looks fine?
JSON parsers report an error at the point where they realize something is wrong, which is often a line or two after the actual mistake — a trailing comma, for example, only becomes a problem once the parser reaches the closing brace and finds no next value where it expected one. If the flagged line looks correct, check the line just before it.
Does this catch duplicate keys, which some validators miss?
Yes. Strict JSON.parse silently keeps only the last occurrence of a duplicate key rather than flagging it as an error, which is exactly how many validators behave too — this tool specifically checks for duplicate keys and reports them, since a silently-overwritten key is a common source of confusing bugs.
What's the most common reason JSON that looks fine still fails?
Two mistakes account for most real-world failures: a trailing comma after the last item in an object or array (legal in JavaScript, not in JSON), and an unquoted or single-quoted object key (JSON requires double quotes around every key, no exceptions). Both are easy to write by hand if you're used to plain JavaScript object literals.