HNC

Installed on a client, the Fabric mod builds a JSON list of the installed mods, each with its id and name, and sends it to the server over a secure plugin channel when the player joins. The data is sent silently, so nothing appears in the player's chat or screen during the join.

A second part, a Paper plugin, has to run on the server. It receives each player's list, stores it against that player's UUID and writes the join to the console log. Admins can then open an in-game menu to inspect the lists. The mod is marked as a Hacking Cheating toolset for transparency on multiplayer servers, and both parts are needed for it to do anything.

Admins can set a keyword blacklist, for example wurst or meteor, so that any mod matching one of the keywords is flagged. Players can still join and play, and the flag only gives the admin information to decide from. The author notes that the approach is meant to avoid guessing and false accusations.