CodePersia

JSON Validator — Check & Validate JSON Syntax Online

Tool processing happens entirely in your browser. Your input is never sent to our servers.

How to Validate JSON

JSON validation checks whether a string is syntactically valid JSON according to the specification (RFC 8259). Valid JSON must follow strict rules: strings use double quotes, keys must be quoted, no trailing commas, no comments, and values must be strings, numbers, booleans, null, objects, or arrays.

Common JSON errors and how to fix them:

  • Trailing commas: {"a": 1, "b": 2,} — remove the comma after the last item
  • Single quotes: {'key': 'value'} — replace with double quotes
  • Unquoted keys: {key: "value"} — add double quotes around the key
  • Comments: // this is a comment — JSON does not support comments; remove them
  • Undefined values: {"key": undefined} — use null instead

When our validator finds an error, it reports the line number and character position along with a descriptive message explaining what went wrong and how to fix it.

After validating your JSON, you can format it for readability or minify it for production. If you need to transmit JSON in a text-only channel, consider Base64 encoding.

How to Use This JSON Validator

  1. Paste or type your input in the editor above
  2. Click the action button or the tool will process automatically
  3. View the result in the output panel
  4. Copy the result with one click using the Copy button

Frequently Asked Questions

It detects all JSON syntax errors: missing or extra commas, unclosed brackets and braces, invalid escape sequences, single quotes, trailing commas, comments, and undefined values. Each error shows the exact position.

This tool validates JSON syntax (is it valid JSON?). JSON Schema validation (does it match a specific structure?) is a different operation that we plan to add as a separate tool.

Common causes: trailing commas after the last item, single quotes instead of double quotes, unquoted keys, comments (// or /* */), or special characters that need escaping. The error message will point you to the exact issue.