Site Valet : Web Tools for Quality, Accessibility, Standards Compliance.
W3C mobileOK Checker : This checker performs various tests on a Web Page to determine its level of mobile-friendliness.
W3C Link Checker : Check links and anchors in Web pages or full Web sites
When can I use... : Compatibility tables for support of HTML5, CSS3, SVG and more in desktop and mobile browsers.
The PHP Coding Standards Fixer : The PHP Coding Standards Fixer tool fixes most issues in your code when you want to follow the PHP coding standards as defined in the PSR-1 and PSR-2 ...
