This is a very simple list for simple sites. More serious sites will have a much longer list. Test all supported browsers. Test with devices: iPhone, iPad, s

This is a very simple list for simple sites. More serious sites will have a much longer list. Test all supported browsers. Test with devices: iPhone, iPad, serveral Android phones (Androd 2.3, 4.1...), Windows Phone Test with several screen widths (responsive design) Test with ad blocker / Ghostery Test for SEO Test title of every page Test internationalization Test accessiblity (good contrast, no small print etc.) Test with reader software Test alt attributes Test low bandwidth Test with keyboard only Test with high load (many requests per sec) Test caching headers Test minification and merging CSS / JavaScript files Test compression of textual files Test favicon and touch icon Test charset Test lang attributes Test HTML5 form features on devices Test offline (when connection gets lots in train for example) Test image and description when the site is added in a Facebook message Etc. etc.