JSON Validator
Real-time JSON validation with detailed error messages
Free online JSON validator and linter. Check JSON syntax instantly with detailed error messages and line numbers. Catch missing commas, unquoted keys, trailing commas, and bracket mismatches. Perfect for APIs, config files, webhooks, and debugging 400 errors. Real-time validation, 100% client-side, no data transmission.
Paste JSON to validate
What Is a JSON Validator?
A JSON Validator (also called JSON Lint or JSON Checker) verifies whether your JSON data follows the correct syntax defined by the JSON specification (RFC 8259). It catches common mistakes like missing commas, unquoted keys, trailing commas, and mismatched brackets — showing you the exact error location so you can fix it quickly.
Common JSON Errors This Tool Catches
- Missing or extra commas between key-value pairs
- Unquoted keys or single-quoted strings (JSON requires double quotes)
- Trailing commas after the last element in an object or array
- Mismatched brackets
{}and[] - Invalid escape sequences in strings
- Comments (JSON does not allow comments, unlike JSON5 or JSONC)
When to Use a JSON Validator
- Before sending JSON payloads to REST APIs or GraphQL mutations
- When debugging 400 Bad Request errors caused by malformed JSON bodies
- Validating configuration files like
package.json,tsconfig.json, or.eslintrc.json - Checking JSON exports from databases (MongoDB, PostgreSQL JSONB columns)
- Verifying webhook payloads from third-party services (Stripe, GitHub, Slack)
JSON Validator vs. JSON Formatter
A JSON Validator tells you whether your JSON is syntactically correct. A JSON Formatter takes valid JSON and reformats it with proper indentation. Use the validator to check for errors first, then format it for readability.