It's the W3C Validator.

by R. Proffitt Moderator - 3/20/12 12:11 PM

In Reply to: 22 errors? by OSSeas

When folk ask me to check a web page for any issue, my first stop is the W3C site. They write the book (or web) on the standards so we want to get the errrors out before we start down the page.
Bob