Postman - The Collaboration Platform for API Development
Proxyman.io - Proxyman is a high-performance macOS app, which enables developers to view HTTP/HTTPS requests from apps and domains.
Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
HTTP Toolkit - Beautiful, cross-platform & open-source tools to debug, test & build with HTTP(S). One-click setup for browsers, servers, Android, CLI tools, scripts and more.
Paw.cloud - Paw is a REST client for Mac.
mitmproxy - mitmproxy is an SSL-capable man-in-the-middle proxy for HTTP.