Packet Sender is a good tool when debugging protocols.

Packet Sender is a good tool when debugging protocols.
Blurb: “[a] free utility to send & receive network packets. TCP, UDP, SSL.”

Written by Dan Nagle (https://twitter.com/naglecode)

https://packetsender.com/

Open Source
https://github.com/dannagle/PacketSender

https://packetsender.com/