JSON Validator
About JSON Validator
The JSON validator checks whether a document is well-formed against RFC 8259 and pinpoints the first syntax error by line and column. Instead of a vague "invalid JSON" from your code, you get the exact spot and reason so you can fix it in seconds.
Validation runs in your browser with no upload, so you can safely check a production API response, a secret-bearing config or a customer record. It is free, instant and requires no account.
It is for anyone debugging a broken payload: a missing comma from a hand edit, an unquoted key, a stray trailing comma, or a truncated response. The tool marks the problem inline and tells you what the parser expected.
How it works
Strict RFC 8259 mode
By default the validator enforces the JSON standard exactly: keys and strings must use double quotes, no comments are allowed, and numbers follow the spec's grammar. This matches how servers, databases and standard parsers will read your data.
Allow trailing commas
Real-world files sometimes carry a trailing comma before a closing bracket or brace. Turn on the trailing-comma option to accept that relaxed style so you can validate config-like input without rewriting it first.
Line and column error markers
When parsing fails, the validator reports the line and column of the first offending character plus a short snippet of the surrounding text, so you can jump straight to the problem instead of scanning the whole document.
What counts as valid
A valid JSON document is a single value — an object, array, string, number, boolean or null — with balanced brackets, quoted keys and no leftover characters after it. The validator confirms all of this in one pass.
Frequently asked questions
What does RFC 8259 strict validation reject?
Comments, trailing commas, single-quoted or unquoted keys, and non-standard number formats like hexadecimal or leading-plus. These are common in JavaScript objects but are not valid JSON.
Should I allow trailing commas?
Only if you are validating a relaxed, config-style file that intentionally uses them. For data that a standard parser will consume, keep strict mode on so you catch commas that would otherwise fail server-side.
The validator points to a line but it looks fine — why?
The error is usually just before the flagged position: a missing comma or an unclosed string on the previous line makes the parser fail at the next token. Check the character right before the marker.
Is it safe to validate sensitive JSON here?
Yes. Validation is entirely client-side. Your input never leaves the browser tab, so tokens and production data stay private.
Does valid JSON mean my data is correct?
It means the syntax is well-formed. It does not check that the values match a schema or your business rules — for that, use the JSON Schema generator and validator.