mitmproxy : mitmproxy is your swiss-army knife for debugging, testing, privacy measurements, and penetration testing. It can be used to intercept, inspect, modify...
Mock Service Worker : Mock by intercepting requests on the network level. Seamlessly reuse the same mock definition for testing, development, and debugging.
HttpWatch : An HTTP Viewer and HTTP Sniffer for IE and Firefox
httpbin : Testing an HTTP Library can become difficult sometimes. PostBin.org is fantastic for testing POST requests, but not much else. This exists to cover al...
toxy is a fully programmatic and hackable HTTP proxy to simulate server failure scenarios and unexpected network conditions, built for node.js/io.js.