Validator

W3C has released Unicorn
, a one-stop tool to help people improve the quality of their Web pages. Unicorn combines four popular tools, including the Markup validator, CSS validator,
mobileOk checker, and Feed validator, with a single interface. This means you can check a Web page with a visit to one url instead of four. Unicorn allows
you to choose all four validation checks at once, or any one of the four individual checks as needed.

Unicorn allows the same three ways to validate your Web site as the individual tools, i.e. you can submit a url to the page to be tested, upload the files,
or enter (cut-and-paste) the code directly into a text box.