JSON validator
Paste a document and find out whether it is valid JSON — and if it is not, exactly where the parser gave up and what it expected instead.
Conversion happens in this browser tab. Nothing is uploaded, logged, or stored.
What is being checked
The validator parses your document against the JSON grammar defined in RFC 8259. If it parses, it is valid; if it does not, you get the line, the column, and a plain explanation of what the parser expected instead. There is no "mostly valid" — JSON is a small, strict grammar with no dialects.
The formatted output on the right is your confirmation. If output appears, the document parsed. If the status bar is red, it did not, and the position given is the first place the parser could not continue — which is usually just after the real mistake, not at it.
What each error actually means
| Message | Cause | Fix |
|---|---|---|
Unexpected token } | A comma before the closing brace | Remove the trailing comma |
Unexpected token ] | A comma before the closing bracket | Remove the trailing comma |
| Unexpected end of JSON input | A brace, bracket, or quote never closed | Format the document and look at the indentation |
Unexpected token ' | Single-quoted string | JSON only allows double quotes |
| Expected property name | An unquoted key | Quote every key |
Unexpected token / | A // or /* */ comment | JSON has no comments — remove them or switch to JSONC/YAML |
| Unexpected non-whitespace character after JSON | Two documents concatenated | Wrap them in an array, or treat the file as JSON Lines |
| Bad escaped character | A lone backslash in a string | Escape it as \\ |
The rules in full
- Strings use double quotes only. Never single quotes, never backticks.
- Every object key is a quoted string, including keys that look like identifiers.
- No trailing comma after the last element of an object or array.
- No comments of any kind.
- Numbers cannot have leading zeros, a leading
+, or a trailing decimal point.NaNandInfinityare not valid JSON. - The literals are
true,falseandnull, lowercase.TrueandNoneare Python, not JSON. - Control characters inside strings must be escaped.
- The document must be a single value. Two objects side by side is not JSON.
Once a document parses, the formatter will lay it out readably and the minifier will strip it back down. For the same checks on YAML, use the YAML validator.
Valid syntax is not the same as correct data. If you need to check that a document has the right fields with the right types, that is JSON Schema — a separate layer on top of syntax validation.
Validating in a pipeline
# fail the build on any malformed JSON in the repo
find . -name '*.json' -not -path './node_modules/*' \
-exec sh -c 'jq empty "$1" || exit 255' _ {} \;
# Python, no dependencies
python -m json.tool config.json > /dev/nullBoth exit non-zero on failure, so either works as a pre-commit hook or a CI step.
Your broken file stays yours
Validators get the rawest input of any tool on this site. When something has already failed, people paste the actual payload — the webhook body, the API response, the log line — complete with tokens, email addresses, and customer records, because they are debugging and not thinking about tidying it first.
That is exactly the case worth designing for. Validation runs in your browser using its own JSON parser. Nothing is transmitted, nothing is stored, and reloading the page discards it.