Checking player installed mod

[blissful quarry]

Is there have way to check installed mod.
Thing I'm doing is mod that checking if player haven't installed ___ mod yet. They can't join ___ server

[rich cove]

you'll need to do a handshake

there's no existing mechanism to do this

even if that's the case, it's extremely easy to bypass a handshake

[main valley]

I made something like that using "ping pong"

When the player joins the server my mod ping server with my empty packet, if I get pong then the server has a mod, if not, then I limit the mod functions