W3C Web Quality Tools
Web Quality Tools – web-based, free, opensource, online or downloadable tools, developed and hosted by W3C.
UNICORN – Improve the quality of the Web
„Improve the quality of the Web“
https://validator.w3.org/unicorn/
Gathers the results of the HTML and CSS validators, as well as other useful services (Internationalization, RSS/Atom feeds, http headers).
MarkUp Validator
„Check the markup (HTML, XHTML, …) of Web documents“
Checks the markup validity of Web documents in HTML, XHTML, SMIL, MathML, etc.
CSS validator
„Check Cascading Style Sheets (CSS) and (X)HTML documents with style sheets“
https://jigsaw.w3.org/css-validator/
Checks Cascading Style Sheets (CSS) and (X)HTML documents that use CSS stylesheets.
Link Checker
„Check links and anchors in Web pages or full Web sites“
https://validator.w3.org/checklink
Looks for issues in links, anchors and referenced objects in a Web page, CSS style sheet, or recursively on a whole Web site.
mobileOK Checker
„Is your Web site mobile-friendly?“
https://validator.w3.org/mobile/
