Mob Spawn Control

Mob Spawn Control is a server-side Fabric mod for controlling Minecraft mob spawning through configuration and in-game admin commands. It supports per-mob spawn rules, global category caps, spawn replacement, attribute scaling, loot scaling, experience scaling, biome spawn additions, and hot-reloaded JSON configuration.

What this mod does

Mob Spawn Control intercepts mob spawning and applies configurable rules before a mob is allowed to enter the world. It can:

• Allow or deny mobs globally, per dimension, per biome, or per spawn type.
• Apply spawn-chance percentages globally, per dimension, or per biome.
• Restrict spawning by Y height, light level, spawn block, time, world age, weather, player distance, and distance from world origin.
• Replace one mob with another when the original mob would have spawned.
• Remove all existing entities of a banned mob from loaded worlds.
• Scale mob health, movement speed, and attack damage.
• Scale loot drops and experience drops.
• Disable experience for mobs created by specific spawn types, such as mob spawners.
• Override vanilla spawn-category population caps.
• Add mobs to biome spawn tables at startup.
• Reload configuration without restarting the server.
• Provide administrative commands with mob, dimension, biome, and spawn-type suggestions.

The mod is intended for survival servers, modpacks, minigame servers, and performance-oriented servers that need predictable mob spawning.

Supported versions

Use the download whose Minecraft version matches your game or server. The 1.21 file will not work on 26.x, and 26.x files will not work on 1.21.

Installation

Client or single-player installation

1. Install the correct version of Minecraft.
2. Install Fabric Loader for that Minecraft version.
3. Install the matching Fabric API release.
4. Download the Mob Spawn Control file for your Minecraft version.
5. Place the downloaded .jar file in the mods folder.
6. Start Minecraft.
7. For single-player testing, open a world and use commands with operator permission where needed.

Server installation

1. Install the correct Minecraft server version.
2. Install the matching Fabric Loader server.
3. Install the matching Fabric API server file.
4. Download the Mob Spawn Control file for your server's Minecraft version.
5. Place the downloaded .jar file in the server's mods folder.
6. Start the server once so the mod can generate its configuration file.
7. Edit config/viper_spawn_control.json.
8. Run /spawncontrol reload to apply changes without restarting.

The configuration file is created at:

config/viper_spawn_control.json

Configuration overview

The configuration has three top-level sections:

Mob IDs use the form minecraft:zombie. Biome and dimension IDs also use namespaced IDs, such as minecraft:plains or minecraft:the_nether.

Complete configuration example

{
  "global_mob_caps": {
    "monster": 70,
    "creature": 10,
    "ambient": 15,
    "underground_water_creature": 5,
    "water_creature": 5,
    "water_ambient": 20,
    "axolotls": 5
  },
  "spawn_rules": {
    "minecraft:zombie": {
      "global_enabled": true,
      "global_spawn_rate_percent": 100.0,
      "disabled_dimensions": [],
      "disabled_biomes": [],
      "disabled_spawn_types": [],
      "dimension_rates": {},
      "biome_rates": {},
      "height_limits": {
        "min_y": -64,
        "max_y": 320
      },
      "light_limits": {
        "min_light": 0,
        "max_light": 7
      },
      "allowed_spawn_blocks": [],
      "time_conditions": {
        "day_only": false,
        "night_only": true,
        "min_world_days": 0
      },
      "attribute_multipliers": {
        "max_health": 1.0,
        "movement_speed": 1.0,
        "attack_damage": 1.0
      },
      "proximity_rules": {
        "min_distance_to_players": 24.0,
        "max_distance_to_players": -1.0,
        "min_distance_to_origin": 100.0,
        "max_distance_to_origin": 10000.0
      },
      "weather_conditions": {
        "rain_only": false,
        "thunder_only": false,
        "clear_only": false
      },
      "replace_with": "",
      "xp_multiplier": 1.0,
      "spawn_type_xp_multipliers": {
        "SPAWNER": 0.0
      },
      "loot_multiplier": 1.0
    }
  },
  "biome_spawn_additions": {
    "minecraft:plains": [
      {
        "mob": "minecraft:polar_bear",
        "weight": 5,
        "min_group": 1,
        "max_group": 2
      }
    ]
  }
}

Spawn-rule configuration table

Each entry under spawn_rules uses a mob ID as its key.

Spawn-type experience multipliers use the spawn reason recorded when the mob is created. For example, "SPAWNER": 0.0 removes experience from spawner-created mobs while leaving naturally spawned mobs of the same type unchanged.

Origin distances use horizontal X/Z distance from the center of the spawn position to world coordinates 0, 0. The calculation is performed separately in each dimension's own coordinate system.

Biome spawn-addition table

Each entry under biome_spawn_additions uses a biome ID as its key and contains a list of spawn entries.

Biome additions are applied during server startup. Restart the server after changing them.

Commands

All commands start with /spawncontrol and require gamemaster-level permission. Mob arguments accept namespaced IDs such as minecraft:sheep; dimension, biome, and spawn-type arguments support suggestions.

The mob argument comes immediately after the subcommand. For scoped commands, the scope follows the mob and value:

/spawncontrol ban minecraft:sheep
/spawncontrol rate minecraft:zombie 50 minecraft:the_nether

Common examples

Ban zombies everywhere and remove existing zombies

/spawncontrol ban minecraft:zombie

Remove experience from spawner mobs only

"minecraft:zombie": {
  "xp_multiplier": 1.0,
  "spawn_type_xp_multipliers": {
    "SPAWNER": 0.0
  }
}

Keep hostile mobs away from spawn

"minecraft:creeper": {
  "proximity_rules": {
    "min_distance_to_players": 24.0,
    "max_distance_to_players": -1.0,
    "min_distance_to_origin": 250.0,
    "max_distance_to_origin": -1.0
  }
}

Replace spiders with cave spiders

/spawncontrol replace minecraft:spider minecraft:cave_spider

Performance notes

• Rules are evaluated only when a mob spawn is attempted.
• Unused proximity checks are skipped.
• Category caps use the configured values during natural-spawn calculations.
• The mod does not add client-side rendering, particles, sounds, or HUD elements.

Enhance your server setup with the other server-side mods in the Fabric Server Essentials organization.