Wireshark

Wireshark is a free and open-source packet analyzer. It is used for network troubleshooting, analysis, software and communications protocol development, and education. It allows users to see what's happening on their network at a microscopic level.

This tool is suitable for network administrators, security professionals, developers, and anyone interested in understanding network traffic. It runs on various operating systems, including Windows, macOS, and Linux, and supports hundreds of protocols.