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

Minecraft	Java	Fabric Loader	Status
1.21 through 1.21.11	21	0.16.x or newer compatible release	Supported
26.1 through 26.1.2	25	0.17.x or newer compatible release	Supported
26.2	25	0.19.3 or newer	Supported
26.3	25	0.19.5 or newer	Supported

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:

Section	Type	Purpose
global_mob_caps	Object mapping spawn-category names to integers	Overrides population limits used for natural spawning categories.
spawn_rules	Object mapping mob IDs to rule objects	Controls where, when, how often, and in what form each mob may spawn.
biome_spawn_additions	Object mapping biome IDs to spawn-entry lists	Adds new biome spawn entries when the server starts.

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.

Field	Type	Description
global_enabled	Boolean	Set to false to ban the mob in every dimension and biome.
global_spawn_rate_percent	Number from 0 to 100	Default spawn chance when no dimension- or biome-specific rate applies.
disabled_dimensions	List of dimension IDs	Prevents the mob from spawning in the listed dimensions.
disabled_biomes	List of biome IDs	Prevents the mob from spawning in the listed biomes.
disabled_spawn_types	List of uppercase spawn reasons	Prevents the mob from spawning through listed mechanisms, such as NATURAL or SPAWNER.
dimension_rates	Object mapping dimension ID to percentage	Overrides the spawn chance for selected dimensions.
biome_rates	Object mapping biome ID to percentage	Overrides the spawn chance for selected biomes. Biome rates take precedence over dimension rates.
height_limits.min_y	Integer	Minimum Y coordinate where the mob may spawn.
height_limits.max_y	Integer	Maximum Y coordinate where the mob may spawn.
light_limits.min_light	Integer from 0 to 15	Minimum light level where the mob may spawn.
light_limits.max_light	Integer from 0 to 15	Maximum light level where the mob may spawn.
allowed_spawn_blocks	List of block IDs	If non-empty, the mob can spawn only when the block below it is in this list.
time_conditions.day_only	Boolean	Allows spawning only during daytime when true.
time_conditions.night_only	Boolean	Allows spawning only during nighttime when true.
time_conditions.min_world_days	Integer	Prevents spawning before the world reaches the selected age in days.
attribute_multipliers.max_health	Number	Multiplies the spawned mob's maximum health.
attribute_multipliers.movement_speed	Number	Multiplies the spawned mob's movement speed.
attribute_multipliers.attack_damage	Number	Multiplies the spawned mob's attack damage.
proximity_rules.min_distance_to_players	Number	Requires spawns to be at least this many blocks from the nearest player.
proximity_rules.max_distance_to_players	Number	Requires a player to be within this distance. Use -1.0 to disable the upper limit.
proximity_rules.min_distance_to_origin	Number	Requires spawns to be at least this many horizontal blocks from world coordinates 0, 0.
proximity_rules.max_distance_to_origin	Number	Prevents spawns farther than this horizontal distance from world coordinates 0, 0. Use -1.0 to disable the upper limit.
weather_conditions.rain_only	Boolean	Allows spawning only while it is raining when true.
weather_conditions.thunder_only	Boolean	Allows spawning only during thunderstorms when true.
weather_conditions.clear_only	Boolean	Allows spawning only during clear weather when true.
replace_with	Mob ID or empty string	Replaces the denied original mob with another mob. Use an empty string to disable replacement.
xp_multiplier	Number	Multiplies experience dropped by the mob. Use 0.0 to disable its experience.
spawn_type_xp_multipliers	Object mapping uppercase spawn reason to multiplier	Overrides xp_multiplier only for mobs born through the specified spawn mechanism.
loot_multiplier	Number	Multiplies the quantity of dropped items.

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.

Field	Type	Description
mob	Mob ID	Mob added to the biome's spawn table.
weight	Integer of at least 1	Relative selection weight for the entry.
min_group	Integer of at least 1	Minimum number of mobs spawned together.
max_group	Integer	Maximum number of mobs spawned together.

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.

Command	Description
/spawncontrol reload	Reloads viper_spawn_control.json from disk.
/spawncontrol info	Displays the executing player's biome, dimension, light level, Y coordinate, and world age.
/spawncontrol ban <mob>	Bans a mob globally and removes existing entities of that type from loaded worlds.
/spawncontrol ban <mob> global	Bans a mob globally.
/spawncontrol ban <mob> dimension <id>	Bans a mob in the selected dimension.
/spawncontrol ban <mob> biome <id>	Bans a mob in the selected biome.
/spawncontrol unban <mob>	Allows a globally banned mob again.
/spawncontrol unban <mob> dimension <id>	Removes a dimension-specific ban.
/spawncontrol unban <mob> biome <id>	Removes a biome-specific ban.
/spawncontrol rate <mob> <percent>	Sets the global spawn-chance percentage.
/spawncontrol rate <mob> <percent> global	Sets the global spawn-chance percentage explicitly.
/spawncontrol rate <mob> <percent> dimension <id>	Sets a dimension-specific spawn-chance percentage.
/spawncontrol rate <mob> <percent> biome <id>	Sets a biome-specific spawn-chance percentage.
/spawncontrol cap <category> <value>	Overrides a natural-spawning category population cap.
/spawncontrol spawntype <mob> <type> <allow|deny>	Allows or denies a particular spawn mechanism, such as NATURAL or SPAWNER.
/spawncontrol height <mob> <min> <max>	Sets permitted Y-coordinate limits.
/spawncontrol light <mob> <min> <max>	Sets permitted light-level limits from 0 to 15.
/spawncontrol attributes <mob> <health|speed|damage> <multiplier>	Sets an attribute multiplier.
/spawncontrol weather <mob> <rain|thunder|clear|none>	Sets a weather restriction.
/spawncontrol replace <mob>	Displays the mob's current replacement.
/spawncontrol replace <mob> <replacement>	Replaces denied spawns with another mob.
/spawncontrol replace <mob> none	Removes the replacement.

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.