Real Mob Filter

Real Mob Filter

Server-side filter for natural spawns, per entity type.

No Fabric API, no commands. No /reload, restart after editing.

Works for any entity, vanilla or not, as long as the spawn goes through the natural spawner (NaturalSpawner).

Config

config/realmobfilter.json (written on first launch)

enabled defaults to false. While it stays false, the filter does nothing.

{
  "enabled": false,
  "entities": {
    "minecraft:phantom": 0.0,
    "minecraft:creeper": 0.25
  }
}

The value is the chance to allow the natural spawn. The roll is uniform in [0, 1).

An invalid id is ignored. A value outside [0, 1] is clamped.

Mobcap

Cancellation happens after Vanilla has picked the type. The attempt is not replaced and there is no second roll.

The mobcap therefore fills more slowly, but it still fills: only with rolls that pass, plus anything that is not in the config.

ToDo

Make the filter point configurable:

• after (current): Vanilla picks, we cancel. Throughput drops.
• before: remove or reweight the type in the biome list, before the roll. Throughput stays at the mobcap rate; only the mix changes.

However, not now; plenty of mods already rewrite that list. Feel free to test and submit a PR.

Where it cuts

Mixin on NaturalSpawner.getMobForSpawn, at the head of the method, before EntityType.create.

Vanilla already does if (mob == null) return;, so the attempt stops before the entity is created, before the collision test, and before finalizeSpawn.

Eggs, spawners, trial spawners, commands and bosses do not go through this method.

Compatibility

• ✅ Real Mobcap: fine. The cap and the filter stack.
• ✅ Carpet: fine.
• ✅ Serilum spawn mods: tested, no issue.
• 🔜 Mob Filter: not tested yet. Can be complementary.