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...
SSL Server Test : This free online service performs a deep analysis of the configuration of any SSL web server on the public Internet.
mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
Sixpack : Sixpack is a language-agnostic ab testing framework
Sixpack makes it easy to run A/B tests across multiple web services written in different languages...
Memorable site for testing clients against bad SSL configs.
