HttpWatch : An HTTP Viewer and HTTP Sniffer for IE and Firefox
Wireshark : Wireshark is the world's foremost network protocol analyzer. It lets you see what's happening on your network at a microscopic level. It is the de fac...
toxy : toxy is a fully programmatic and hackable HTTP proxy to simulate server failure scenarios and unexpected network conditions, built for node.js/io.js.
mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
Postman : Save requests and organize your APIs into Collections. Create and send any HTTP request using the awesome Postman request builder. Write your own test...