SEO Tool

HTML Validator

Validate the markup of any public URL against the W3C HTML specification. Powered by the W3C Nu Html Checker — the same engine behind validator.w3.org/nu/, just wrapped in a faster UI.

About

The Nu Html Checker is the official HTML5 validator (the same engine that powers validator.w3.org/nu/). It reports parse errors, invalid attribute values, accessibility hints, and document structure issues. We proxy the request from the edge via validator.nu — your browser never talks to the validator directly.

JSON: /api/html-validate?url=https://example.com