🗺️Using Coordinates

"How can I get a unique ID for every world / server / realm / etc to store my data under"

Coordinates are Java records that contain an ID based on the connection, and a generated human-readable name. Some may also contain extra data such as a singleplayer world's directory name, or a multiplayer server's address.

Coordinate Type	Example ID	User-friendly Name
Singleplayer / LAN host	singleplayer/New World	Singleplayer: New World
LAN (remote player)	lan/Herobrine - New World	LAN: Herobrine - New World
Multiplayer Server	multiplayer/mc_hypixel_net	Multiplayer: Hypixel
Realm Server	realms/4201C8930F12E800	Minecraft Realms: Builder's Palace

User-friendly names for Singleplayer, Multiplayer and Realms coordinates are localized based on the user's current language.

A common use point might be on server connect, such as in Fabric's ClientPlayConnectionEvents#JOIN:

ClientPlayConnectionEvents.JOIN.register((handler, sender, client) -> {
    Coordinate.getCurrent().ifPresent(coordinate -> {
        String id = coordinate.id();
        
        // load data, check server id, etc
    });
});

Coordinates aren't available duringClientPlayConnectionEvents#DISCONNECT - you may want to save the one you use loading data alongside the data itself. You can see this being done in the Example Notes Mod.

If you're making a mod specifically to work with a server, you can easily refine a coordinate and check it's address:

if (coord instanceof Coordinate.Multiplayer multi
    && multi.address().contains("hypixel.net")) {
    // hypixel specific stuff
}