JSON Validator

Validate JSON syntax with detailed error reporting. Inspect JSON structure tree. Validate JSONL line by line. Free, instant, 100% private.

About JSON Validator

Validate JSON and JSON Lines data with detailed error reporting. Parses SyntaxError messages to extract exact line and column positions. On success, explore the parsed JSON structure tree showing keys, types, nesting depth, and sample values. All processing stays in your browser.

Detailed Error Reporting

Shows exact line, column, and what was expected vs found. Fix JSON errors quickly without hunting through brackets.

JSONL Validation

Validate each line of JSON Lines data individually. Perfect for streaming data, log files, and bulk processing pipelines.

Structure Tree View

Explore parsed JSON visually. See all keys, their types, nesting depth, and sample values in an expandable tree format.

File Upload

Upload .json or .jsonl files for validation. All processing stays in your browser — nothing is uploaded to any server.

📋 Common Use Cases

Pre-Commit Checking

Validate JSON, HTML, or other structured data before committing to your repository. Prevent broken configs from reaching production.

API Response Verification

Validate JSON responses from your API endpoints during development and testing. Ensure your data contracts are well-formed.

Configuration Debugging

Find syntax errors in JSON configuration files, package.json, or manifest files. Get line-level error details for quick fixes.

Code Quality Assurance

Validate HTML for accessibility and standards compliance. Catch missing tags, invalid attributes, and structural issues.

🪜 How to Use This Tool

  1. Paste code or data to validate
    Enter JSON, HTML, or other structured text into the input area. Syntax errors are highlighted in real time.
  2. Review error details
    See line numbers, column positions, and descriptions for each issue. Click errors to jump to the problematic location.
  3. Fix and revalidate
    Edit in place and see validation results update automatically. Iterate until your code is clean.
  4. Copy validated code
    Once valid, copy the code for use in your project. Some validators also format/beautify the output.

📚 Related Guides

Frequently Asked Questions

Are these dev tools free?▼
Yes. All dev tools are completely free. No signup, no account.
Is my data sent to a server?▼
No. Base64 encoding, URL encoding, JWT decoding, hash generation, and regex testing all happen in your browser. Your tokens and secrets stay on your device.
Can I decode JWTs safely?▼
Yes. JWT decoding happens entirely in your browser. The token never leaves your device. Only the header and payload are decoded — signatures are not verified server-side.