SSL Server Test : This free online service performs a deep analysis of the configuration of any SSL web server on the public Internet.
boomerang : boomerang is a piece of javascript that you add to your web pages, where it measures the performance of your website from your end user's point of vie...
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
Pa11y : Monitor the accessibility of your websites with pa11y-dashboard, and protect against accessibility errors creeping into your codebase.
Skipfish : Skipfish is an active web application security reconnaissance tool. It prepares an interactive sitemap for the targeted site by carrying out a recursi...
webhint is a linting tool that will help you with your site's accessibility, speed, security and more, by checking your code for best practices and common errors. Use the online scanner or the CLI to start checking your site for errors.