Spawn Doctor

Spawn Doctor gives the server owner a read-only command that inspects the area where a player is standing and reports the reasons a correctly built farm may be silent. It calls out causes that are close to certain, such as the Peaceful difficulty, doMobSpawning being off, or the surface spawn habit that makes many farms look broken. A player can stand where they expect spawns and run the command to get the diagnosis on demand.

The mod also reports conditions that are harder to see, including hostile mobs loaded far away that consume the spawn budget, and an AFK spot placed too close to the spawning ring. Spawn Doctor measures these through a ring simulation over distances from 24 to 128 blocks and states the universal spawn rules it applies. It does not claim an exact mob-cap number, because the cap formula changes between versions, so it reports what is likely wrong rather than a precise value. Overlays from other mods only show light level, and nothing else in the catalog explains a silent farm this way.

The mod is installed on the server only. Players who join need nothing, and the server runs it with Fabric API present. Files are published for Fabric, Forge and NeoForge, with 1.20.1 and 1.21.1 as the game versions covered. The mod is not open source; it is released under All rights reserved, though the source code is public.