Data-Driven Spawn Rules

Data-Driven spawning allows creators to adjust the spawn conditions of mobs within Minecraft: Bedrock Edition, providing the tools to determine when, where, and how mobs spawn in the world. Let's take a closer look at how data-driven spawning works.

Spawn Rules

First and foremost, all Spawn Rules JSON files must have an ID that follows the "namespace:name" convention. Note that the minecraft namespace is reserved for vanilla Minecraft rules.

When changing an existing mob, use the ID that appears in the entity JSON for that entity. When creating your own mob, make sure all of the entity's JSON files use the same ID.

Secondly, the pool used for population control must be defined. There are four pools that entities can be assigned to (animal, water_animal, monster, and cat), and each has its own spawn limit. By assigning an entity to a pool, it will spawn as long as that pool hasn't reached the spawn limit.

Important

The 'cat' pool functions differently than the other 3 population pools. Cat spawn rules and limits are based upon the amount within a village.

Note

There are 2 more pools located within the game files, Villager and Pillager. However, these are not currently used by any entities.

Components

The following components provide the specifics in determining the ways in which spawns occur, from specifying which spawns occur by difficulty to setting the probability of spawned entities to mutate; this is where the potential for magic occurs.

Name	Description
minecraft:biome_filter	Allows players to specify which biomes the mob spawns in. Check on minecraft:biome_filter to see which Biome Tags exist, and what each biome is tagged as.
minecraft:brightness_filter	Allows players to set the light level range that causes the mob to spawn.
minecraft:delay_filter	Allows players to set mobs spawn with specified time delays.
minecraft:density_limit	Allows players to specify the amount of mobs to spawn in certain locations.
minecraft:difficulty_filter	Allows creators to set which mobs spawn depending on difficulty level.
minecraft:disallow_spawns_in_bubble	Allows creators to keep entities from spawning in bubbles.
minecraft:entity_types	This is a specific type of JSON object used by Minecraft: Bedrock Edition to encapsulate entity data that can be used in certain behaviors and components.
minecraft:height_filter	Allows players to set mob spawning within specific heights of the map.
minecraft:herd	Allows players to determine the herd size of animals.
minecraft:mob_event_filter	Allows players to spawn mobs on a pillager, wandering trader, or ender dragon event.
minecraft:operator	Defines arithmetic operators in order to compare the values of two given data points.
minecraft:permute_type	Allows players to specify the permutations of a mob that will spawn.
minecraft:player_in_village_filter	Allows players to be filtered by whether they are in a village or not, using distance and the village border definitions.
minecraft:spawn_event	Event related to the spawning of an entity.
minecraft:spawns_lava	Determines if an entity spawns on lava.
minecraft:spawns_on_block_filter	Allows an entity to spawn on a particular block.
minecraft:spawns_on_block_prevented_filter	Prevents an entity from spawning on a particular block.
minecraft:spawns_on_surface	Allows an entity to spawn on the surface.
minecraft:spawns_underwater	Allows the mob to spawn underwater.
minecraft:weight	Allows players to set a priority for how often that mob should spawn.
minecraft:world_age_filter	Allows players to set mob spawns after a specified amount of time has passed within a world.

Example Spawn Rules for the zombie

{
  "format_version": "1.8.0",
  "minecraft:spawn_rules": {
    "description": {
      "identifier": "minecraft:zombie",
      "population_control": "monster"
    },
    "conditions": [
      {
        "minecraft:spawns_on_surface": {},
        "minecraft:spawns_underground": {},
        "minecraft:brightness_filter": {
          "min": 0,
          "max": 7,
          "adjust_for_weather": true
        },
        "minecraft:difficulty_filter": {
          "min": "easy",
          "max": "hard"
        },
        "minecraft:weight": {
          "default": 100
        },
        "minecraft:herd": {
          "min_size": 2,
          "max_size": 4
        },
        "minecraft:permute_type": [
          {
            "weight": 95
          },
          {
            "weight": 5,
            "entity_type": "minecraft:zombie_villager_v2"
          }
        ],
        "minecraft:biome_filter": {
          "test": "has_biome_tag", "operator": "==", "value": "monster"
        }
      }
    ]
  }
}

Vanilla Entity Spawn Rules

Below is a list of all available spawn rules for Vanilla Behavior Pack entities as of the publication of this article.

Entity Spawn Rules JSON
axolotl
bat
bee
blaze
cat
chicken
cod
cow
creeper
dolphin
donkey
drowned
enderman
fox
ghast
glow_squid
goat
guardian
hoglin
horse
husk
llama
magma_cube
mooshroom
ocelot
panda
parrot
phantom
pig
piglin
pillager
polar_bear
pufferfish
rabbit
salmon
sheep
skeleton
slime
spider
squid
stray
strider
tropicalfish
turtle
witch
wither_skeleton
wolf
zombie_pigman
zombie