To validate your HTML, XHTML or CSS documents you can use the online validation service provided by the The World Wide Web Consortium (W3C).
This is a free service that checks HTML, XHTML and CSS documents for conformance to W3C Recommendations and other standards. The validator will check the file and flag any errors it discovers.
You can check files that are already online as well as files on your
Once you have created files that validate correctly, you can display the
"Valid HTML", Valid XHTML" or "Valid CSS" icons on you website.