“Build better websites” with Webhint. Webhint is open source and offers many features such as testing a site’s accessibility, speed, security, and more. Webhint is fully customizable with the ability to “ignore 3rd-party code, prioritize your users’ browsers, and control the results with minimal setup.”
Want even more Webhint flexibilty, then follow the developers’ guide to create your own new rules with the possibilty also of adding your rules to Webhint’s open source.
Visit Webhint for more information.