ValidatorJSON
Verify whether a JSON string is syntactically valid and find any errors instantly with this free online JSON validator. Invalid JSON breaks API calls, causes config file parse failures, and creates hard-to-debug application errors. Before deploying configuration files, submitting API data, or importing JSON records, validating the structure ensures it can be parsed correctly by any JSON parser.
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JSON Validator
Interactive developer tools engine
How To Use JSON Validator
- Paste the JSON text you want to validate into the input field.
- Click validate or wait for automatic validation to run.
- If the JSON is valid, a success message confirms it is syntactically correct.
- If errors are found, the validator displays the location and nature of each error.
- Fix the reported issues and re-validate until the JSON passes validation.
Frequently Asked Questions
Does this validate JSON structure and syntax?
Yes. The validator checks whether the JSON string can be parsed according to the official JSON specification (RFC 8259). It verifies correct use of double quotes for strings, proper bracketing of arrays and objects, valid value types (strings, numbers, booleans, null, arrays, and objects), and absence of illegal syntax like trailing commas and JavaScript comments.
What are the most common JSON syntax errors?
The most frequent JSON errors include: using single quotes instead of required double quotes around string keys and values, adding a trailing comma after the last element in an array or object, including JavaScript-style comments (// or /* */), having unmatched or missing curly braces or square brackets, and using undefined or NaN as values (these are JavaScript-specific and not valid JSON).
Can JSON have comments?
No. Standard JSON does not support comments of any kind. This is one of the most common surprises for developers coming from JavaScript or other languages where inline comments are normal. Some non-standard extensions like JSONC (JSON with Comments) allow comments, but standard JSON parsers will reject them. If you need inline documentation in a configuration file, consider YAML instead of JSON.
What is the difference between JSON validation and JSON schema validation?
Syntax validation checks whether the text is valid JSON — correct structure, quotes, and brackets. JSON Schema validation goes further and checks whether the data matches a defined schema — for example, verifying that a required field exists, that an age value is a number above 0, or that an email field matches an email format. This tool handles syntax validation; JSON Schema validation requires a separate schema definition.
Why might my JSON be valid but still cause errors in my application?
Syntactically valid JSON can still cause application errors if the data does not match what your code expects — for example, a missing required field, a string where a number is expected, or a null value where your code assumes an object exists. These are data contract or schema errors, not syntax errors. Use JSON Schema validation or defensive programming (null checks and type validation) to catch these issues.
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