HTML debugging

The best way to debug is to pass your HTML page through the Markup Validation Service . A markup verification service created and maintained by W3C (an organization that sets standards for HTML, CSS, and other web technologies). Load an HTML document into this webpage and run it, the webpage will return an error report. 

Web pages can accept URLs, upload an HTML document, or directly enter some HTML code.

Active learning: validating HTML documents

 Try it with the debug-example.html above  :

1. Open the Markup Validation Service in your browser   .
2. Select the  Validate by Direct Input  tab.
3. bodyCopy and paste the code of the entire sample document (not just part of it) into the middle text box.
4. Click the  Check  button.

A list of errors and other information will be returned.