JSON Validator Online
Validate your JSON data instantly with detailed error reporting. Paste or type JSON and get immediate feedback on syntax errors with line numbers and descriptions.
Common JSON syntax errors
The most frequent JSON errors are: trailing commas after the last item in arrays or objects, single quotes instead of double quotes, unquoted keys, missing commas between items, and unclosed brackets or braces. JavaScript object syntax is not valid JSON — keys must be double-quoted strings.
JSON syntax rules
Valid JSON must follow these rules: strings use double quotes only, keys must be double-quoted strings, no trailing commas, no comments, numbers cannot have leading zeros, and the root value must be an object or array (though modern parsers accept any JSON value).
Frequently Asked Questions
What makes JSON invalid?
Common causes: trailing commas, single quotes, unquoted keys, comments, undefined/NaN values, and mismatched brackets. JSON is stricter than JavaScript object literals.
Is JSON with comments valid?
No. Standard JSON (RFC 8259) does not support comments. Some parsers accept JSONC (JSON with Comments), but it is not valid JSON. Remove comments before validating.