DevToolKit

JSON Validator — Check Syntax & Show Errors with Line Numbers [2026]

Validate JSON syntax instantly. Get detailed error messages with exact line and column numbers. Highlights common mistakes like trailing commas and missing quotes. Free, browser-based.

What is JSON Validator?

JSON Validator is a free online tool that checks whether your JSON data is syntactically correct. It parses the input and reports errors with precise line and column numbers, making it easy to find and fix issues like trailing commas, missing quotes, or unmatched brackets.

How to Use JSON Validator

Paste your JSON into the editor. The tool validates it in real time and shows a green checkmark if valid or a detailed error message with the exact line number and column where the problem is. Click "Load Sample" to try an example. Click "Fix & Format" to auto-format valid JSON with your preferred indentation.

How JSON Validator Works

The tool uses the browser's built-in JSON.parse() for validation. When parsing fails, it extracts the error position from the exception message and maps it to line and column numbers by scanning the input text. Valid JSON is pretty-printed with syntax highlighting.

Common Use Cases

  • Debugging malformed API responses or request bodies
  • Checking JSON config files before deploying
  • Validating JSON payloads from third-party services
  • Finding syntax errors in hand-edited JSON files
  • Verifying JSON output from code generators

Frequently Asked Questions

What types of JSON errors does this tool detect?▼

It detects all syntax errors including missing or extra commas, unquoted keys, single-quoted strings, trailing commas, unmatched brackets or braces, and invalid escape sequences.

Does it show the exact line where the error is?▼

Yes. When a syntax error is found, the tool displays the line number and column number, and highlights the problematic line in the editor so you can find it quickly.

Can it fix JSON errors automatically?▼

The tool can format valid JSON but cannot auto-fix syntax errors, since the intended fix is ambiguous. It shows you exactly where the error is so you can fix it yourself.

Is my data safe?▼

Yes. All validation runs in your browser using JavaScript. No data is sent to any server.

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