mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
Webhook Tester : Webhook Tester allows you to easily test webhooks and other types of HTTP requests.
Mockbin : Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.
Frisby.js : Frisby is a REST API testing framework built on node.js and Jasmine that makes
testing API endpoints easy, fast, and fun. Read below for a quick overv...
HttpWatch : An HTTP Viewer and HTTP Sniffer for IE and Firefox
toxy is a fully programmatic and hackable HTTP proxy to simulate server failure scenarios and unexpected network conditions, built for node.js/io.js.