Free HTML / CSS / Link Validation page

[KenR]

Use this site to check your site for errors.

In a nutshell: this page lists HTML validators (which check HTML code for standards compliance and errors), CSS validators (which check Cascading Style Sheets for errors and standards compliance), browser compatibility checkers (checks your page to see if it is compatible with various browsers), broken link (or dead links) checkers, accessibility checking (check if your web page is accessible to people with disabilities)...

http://www.thefreecountry.com/webmaster/htmlvalidators.shtml

[Clive]

Thanks for pointing this site out. A great help to a newbie site builder like me. My tiny site has numerous errors

[Josh]

The only two validators I use are:

http://jigsaw.w3.org/css-validator/

http://validator.w3.org

[steeladept]

Personally, I find the validators in the WebDeveloper toolbar for Firefox more than sufficient.  I believe they use the w3.org validators for CSS and HTML, but I am not sure.  Regardless, with that and firebug, it is difficult for me to see the need for another tool for XHTML pages.