SelectOracle is a teaching tool and CSS validator created by friends-of-Webmonkey Eric Meyer and Kevin Jacobs. We’re not really sure which use is cooler (the validating or the teaching), but ...

HTML/XHTML markup validator CSS validator Atom or RSS feed validator mobileOK, which tells you how friendly your site is to mobile visitors When you visit the Unicorn page, you'll see a dropdown ...

The CSS Validation Service checks for strict adherence to the DTDs (document type definitions) that formally define HTML, so a page that passes the validation tests will truly be standard-compliant.