Validator Knowledge Base

JSON Validator Online: Free RFC 8259 Syntax Checker

Validate JSON syntax instantly with our free online JSON validator. Detects unexpected tokens, trailing commas, missing quotes, and unclosed brackets with exact line numbers.

Why JSON Validation Matters

A single misplaced comma or missing quotation mark can break an entire application. JSON validation against RFC 8259 catches these errors before they reach production.

What Our JSON Validator Checks

  • Unexpected tokens: Single-quoted strings, unquoted keys, JavaScript comments.
  • Trailing commas: Commas after the last key in objects or last item in arrays.
  • Unclosed brackets: Missing } or ] at the end.
  • Invalid escape sequences: Malformed Unicode or control characters.
  • Number format violations: Leading zeros, NaN, Infinity values.

How to Validate JSON Online

  1. Paste your JSON text into the validator input.
  2. Validation runs automatically as you type.
  3. Errors are highlighted with the exact line and character position.
  4. Green checkmark confirms valid RFC 8259 compliant JSON.

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Frequently Asked Questions

What is the difference between JSON linting and JSON validation?

JSON linting typically refers to style checking (formatting), while JSON validation strictly checks that the data conforms to RFC 8259 syntax rules. JSON2X performs syntax validation and reports parse errors.

Does the validator support JSON Schema validation?

Basic syntax validation is built-in. For JSON Schema (Draft-07) validation, use our JSON Schema Generator tool.

Can I validate JSON from an API response?

Yes. Copy the raw response body from browser DevTools and paste it into the validator input.

Is JSON5 or JSONC (comments) supported?

No. The validator strictly follows RFC 8259, which does not allow comments, single quotes, or trailing commas.

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