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...
Insomnia REST Client : Insomnia is a cross-platform REST client, built on top of Electron.
SPOF-O-Matic : Chrome extension for detecting and simulating frontend Single Points Of Failure. Detects likely third-party single points of failure as you browse and...
Memorable site for testing clients against bad SSL configs.