https://0xbharath.github.io/art-of-packet-crafting-with-scapy/scapy/creating_packets/ index.html

https://scapy.readthedocs.io/en/latest/introduction.html#about-scapy

Scapy is a powerful and interactive packet manipulation tool that allows the security professional to easily and programmatically manipulate the TCP header length and checksum using arbitrary numbers and to observe how the proprietary service responds. Scapy can craft, send, receive, and analyze packets of various protocols, such as TCP, UDP, ICMP, or IP. Scapy can also modify any field of any layer of a packet, such as the TCP header length and checksum, which are used to indicate the size and integrity of the TCP segment. Scapy can also display the response packets from the target system, which can reveal how the proprietary service handles the invalid packet.