Free JSON Validator Online — Check, Lint & Validate JSON Syntax

This free online JSON validator checks your JSON for syntax errors, structural issues, and schema compliance — all in your browser with no upload required. Paste an API response, config file, or any JSON string to instantly lint and validate JSON online. Common errors like missing commas, unquoted keys, trailing commas, and mismatched brackets are flagged with the exact line and character position. Use it to check JSON validity online before pushing to production or sharing with your team. AllOneTools never receives your data.

Beyond syntax checking, you can use this tool to validate JSON against a JSON Schema — the standard for defining the shape, required fields, and data types in a JSON document. Use this online json validator with schema support: paste your JSON in the input panel alongside your schema definition to check for structural compliance without any server-side processing.

JSON Schema validation is essential when working with APIs that enforce a contract, configuration files with required fields, or any workflow where data integrity must be verified before ingestion. Our online JSON schema validator supports draft 4, draft 6, and draft 7 — the most widely used schema versions in production systems today.

Looking for a specific use case? Use validate JSON schema online to catch type mismatches and required-field errors, or use the basic syntax mode to check JSON validity online without any schema.

When you validate JSON online and see an error, it's almost always one of these six issues:

1. Trailing comma — a comma after the last item in an array or object: {"a": 1,} is invalid.
2. Single quotes — JSON requires double quotes for all strings and keys: {'key': 'value'} is invalid.
3. Unquoted keys — unlike JavaScript, JSON keys must always be quoted: {key: "value"} is invalid.
4. Missing comma between items — every element in an array or object must be separated by a comma.
5. Mismatched brackets — every { needs a } and every [ needs a ].
6. Undefined or NaN values — JSON only allows strings, numbers, booleans, null, arrays, and objects. undefined and NaN are not valid JSON.

• Verify API responses before processing in applications.
• Debug JSON configuration files for proper structure—use it like a quick json syntax checker in the loop.
• Ensure JSON data integrity before database operations.
• Check exported JSON from various systems; combine with CI to validate json against schema when contracts matter.
• Validate JSON before sharing with team members or integrating with services.

1. Paste your JSON data into the editor (json lint online style feedback comes from the parser message).
2. Alternatively, upload a JSON file.
3. Click the 'Validate' button to check if json is valid.
4. Review the validation results immediately.
5. If errors are found, correct them based on the detailed error messages.

• Strict JSON syntax validation (json syntax checker) with line-level parser errors.
• Detailed error messages with specific location information.
• Support for uploading and validating JSON files.
• Syntax highlighting for better readability and error detection.
• Instant feedback with clear status indicators.
• Support for large JSON files with efficient processing.
• Privacy-focused with client-side processing only.

• Pay attention to missing commas, which are common JSON syntax errors.
• Ensure all opening brackets have corresponding closing brackets.
• Check that property names are enclosed in double quotes.
• Verify that string values are also properly quoted.
• Use the syntax highlighting feature to better visualize your JSON structure—especially when mirroring a json syntax checker workflow.