Screenfly : Test Your Website at Different Screen Resolutions
Diagnostic.css : Diagnostic.css is a stylesheet which allows the user to test for common errors in a page's markup.
Also : https://github.com/karlgroves/diagnostic.css
Lighthouse : Lighthouse is an open-source, automated tool for improving the quality of web pages. You can run it against any web page, public or requiring authenti...
Maestro : Maestro is the easiest way to automate UI testing for your mobile app.
W3C mobileOK Checker : This checker performs various tests on a Web Page to determine its level of mobile-friendliness.
The mobiReady testing tool evaluates mobile-readiness using industry best practices & standards.