JSON Validator — Check JSON Syntax Free Online

How to use

1. Paste JSON — Paste the JSON you want to validate into the input area
2. Click Validate — The tool parses your JSON and checks for syntax errors
3. Review Results — See whether your JSON is valid, or find the error location

What Is a JSON Validator?

A JSON validator checks whether a text string conforms to the JSON specification (RFC 8259). Valid JSON can be parsed by any JSON-compliant parser in any programming language. Invalid JSON will cause parsing errors that can break applications, APIs, and data pipelines.

This tool uses the browser's native JSON.parse() method, which implements the full JSON specification. When parsing fails, it reports the error message and approximate position, helping you locate and fix the problem quickly.

Common JSON Syntax Errors

JSON has a strict syntax that differs from JavaScript object literals. These are the most frequent mistakes:

• Trailing commas: {"a": 1,} — JSON does not allow commas after the last element
• Single quotes: {'key': 'value'} — JSON requires double quotes for strings
• Unquoted keys: {key: "value"} — All keys must be double-quoted strings
• Comments: JSON does not support comments of any kind
• Missing brackets: Unclosed arrays or objects cause parsing failures

Why Validate JSON?

Invalid JSON can cause silent failures in applications. An API that receives malformed JSON may return cryptic error messages. A configuration file with a syntax error may prevent an entire application from starting. Validating JSON before using it catches these issues early.

• API development: Verify request and response payloads are valid before sending
• Configuration files: Check config files (package.json, tsconfig.json) before deploying
• Data import: Validate JSON data files before importing into databases
• Debugging: Quickly determine if a problem is caused by malformed JSON

JSON vs JavaScript Objects

JSON looks similar to JavaScript object literals but has stricter rules. JavaScript allows single quotes, unquoted keys, trailing commas, and comments — JSON does not. This difference catches many developers off guard when they hand-write JSON instead of generating it programmatically.

Error Position Reporting

When validation fails, this tool reports the approximate line and column number of the error. This helps you navigate to the exact location of the problem, especially in large JSON files with hundreds of lines. The position is calculated from the native parser's error message.

Privacy

All validation runs locally in your browser. Your JSON data never leaves your device. You can safely validate sensitive configuration files, API responses containing credentials, and private data.

Need to format valid JSON? Try our JSON Formatter. Convert JSON to spreadsheet format with our JSON to CSV Converter.

Frequently asked questions

What makes JSON invalid?

Common issues include trailing commas, single-quoted strings, unquoted keys, missing brackets, and comments. JSON follows a strict specification (RFC 8259) that requires double-quoted strings and no trailing commas.

Can this fix invalid JSON?

This tool identifies errors and their approximate location but does not auto-fix them. Use the error details to locate and correct the issue manually.

Does it validate JSON Schema?

No. This tool validates JSON syntax only. It checks whether the text is parseable as JSON, not whether it conforms to a particular schema definition.

Is my data safe?

Yes. Validation happens entirely in your browser using the native JSON.parse() method. No data is sent to any server.

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