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
WebPagetest : Run a free website speed test from multiple locations around the globe using real browsers (IE and Chrome) and at real consumer connection speeds.
Yellow Lab Tools : Online test to help speeding up heavy web pages
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...
TruffleHog : TruffleHog is an open-source SAST (static application security testing) tool for detecting secrets in various sources. While GitHub and GitLab reposit...
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.