Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
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.
code-ray - Live debugging tool for software developers
Postman - The Collaboration Platform for API Development
Reactime - Time travel debugging tool, visualizing and tracing state