webhint : 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 co...
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...
The Coach : The coach helps you find performance problems on your web page. Think of the coach as a modern version of YSlow. The coach will give advice of how you...
Subgraph Vega : Vega is an open source platform to test the security of web applications. Vega can help you find and validate SQL Injections, Cross-Site Scripting (XS...
Monitor the accessibility of your websites with pa11y-dashboard, and protect against accessibility errors creeping into your codebase.