Have that friend that just wont quit cheating?
I have just the mod for you! Presenting CheatNoMore. This mod ensures that all commands sent to the server will be logged in chat, eliminating any chance for players to conceal cheats.
It will log
Gamemode changes
Commands
Gamerule updates
TLDR, how it works is it makes it so any time a command is sent it will log in chat so anyone can see it, and any command send is stored so you can lookup what commands someone has used!

