Server PreCheck

On connection, the client sends its mod list and the server validates it against rules set in the configuration. In blacklist mode, which is the default, every mod is allowed except those named in the client mod blacklist; the blacklist ships with entries for aristois, bleachhack, meteor-client and wurst. In whitelist mode, enabled by setting USE WHITELIST ONLY to true, only the mods listed in the client mod whitelist are accepted. A whitelist can be generated by running the serverprecheck build on a client that has only the acceptable mods, which copies the mod list to the clipboard.

Access can also be adjusted per player. Adding a player's UUID to the exempt players list lets that player bypass the checks. Message texts such as the header for unauthorized or missing mods can be customized, and the message keys support translation. Mod IDs are read from the fabric.mod.json file inside each mod's JAR, and player UUIDs can be looked up on NameMC or taken from the server logs.