Free JSON Validator
Validate JSON syntax in real-time. Get detailed error messages with line numbers, auto-fix common issues, and format/minify JSON instantly.
About JSON Validation
JSON (JavaScript Object Notation) is a lightweight data format widely used in web APIs, configuration files, and data storage. Valid JSON must follow strict syntax rules: keys must be strings in double quotes, values must be properly typed, and there must be no trailing commas.
Common JSON Errors:
- Single quotes instead of double quotes: JSON only allows double quotes for strings
- Trailing commas: The last item in an object or array cannot have a comma
- Unquoted keys: Object keys must always be in double quotes
- Undefined values: JSON doesn't support undefined; use null instead
- Comments: JSON doesn't support comments (though some tools allow them)
What is valid JSON?
Valid JSON must be one of these types: object ({}), array ([]), string (""), number, boolean (true/false), or null. All strings and object keys must use double quotes. Numbers cannot have leading zeros. Whitespace is allowed between elements.
What does "fix common issues" do?
The fix feature attempts to auto-correct common errors: trailing commas, single quotes to double quotes, unquoted keys, and undefined values to null. It's a best-effort tool and may not fix all issues—review the result carefully.
How do I validate JSON in my application?
In JavaScript: use JSON.parse() and catch errors. In Node.js: fs.readFileSync() + JSON.parse(). In Python: json.loads() or json.load(). Most languages have built-in JSON validation libraries.