Spawn Rules

A server-side Fabric mod that lets you block specific mobs and animals from spawning. It cancels spawns early in the tick loop to save server performance.

Key features:

• Blocks spawns before the mob entity is created, which reduces server CPU load.
• Prevents "Can't spawn entity of type" warning spam in the console logs.
• Player-spawned entities (spawn eggs, summon commands, breeding, buckets, and portal travel) are always allowed.
• Includes an in-game GUI to change settings without editing files.

Run the command /spawnrules config in-game (requires operator level 2).

1. A menu will open showing all survival mobs in the game (including modded ones).
2. Hovering over a mob shows if it is allowed or blocked in the Overworld, Nether, and End.
3. Click any mob to toggle its spawn status for those dimensions.
4. Changes save to disk and update in memory immediately.

You can also edit the config file directly at config/spawnrules.json. Here is an example config that blocks zombies in the overworld:

{
  "dimensions": {
    "minecraft:overworld": {
      "blocked_types": [
        "minecraft:zombie"
      ],
      "blocked_categories": []
    }
  }
}

• blocked_types: A list of entity IDs (like minecraft:zombie) to block in that dimension.
• blocked_categories: A list of categories to block. The categories are:
  • monster (zombies, creepers, skeletons, etc.)
  • creature (cows, pigs, sheep, etc.)
  • ambient (bats)
  • water_creature (squids, dolphins)
  • water_ambient (tropical fish)
  • axolotls
  • underground_water_creature (glow squids)

• /spawnrules config - Opens the visual settings GUI (Requires OP level 2).
• /spawnrules reload - Reloads the settings from the configuration file (Requires OP level 2).