HTML checking

Rocket Validator checks the HTML markup on your web pages using the open source Nu HTML Checker (v.Nu), which is the backend of,, and

We host the validator in our own servers, so we can scale them as needed and let you avoid being blocked by excessive usage.

To know more about the Nu HTML checker, visit:

For each page in your validated sites, Rocket Validator will show:

  • Severity of the issue. Error or warning.
  • Error message. A quick explanation of the issue.
  • Line and column. Showing the place where this issue is found in your page, with direct links to the source code.
  • Excerpt. A code snippet from your page showing the affected code.
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Validate Accessibility and HTML5 on large sites, starting at $24/week. Start here