Spawn

Spawning refers to players and mobs being created and placed in the game world. Players will respawn at their spawn point, or at the bed they last slept in upon death. Mobs will despawn upon death.

Player spawning
Since Minecraft version 1.3, players in both singleplayer and multiplayer will spawn, by default, anywhere within a 20x20 area centered at the world spawn point. An individual player can change their spawn point by merely lying in a bed—they do not have to go to sleep (which can only happen if all players use a bed at the same time).

On multiplayer servers, a 33x33 block area centered at the default spawn point, and spanning the full height of the map, is "protected". Players, other than server operators, cannot place or destroy blocks in the protected area, use doors, activate switches other than pressure plates, or open chests or other blocks which contain items. Creepers can still destroy terrain in the protected area and TNT placed outside of the protected area will destroy surrounding blocks as usual. Along with this, portals from the nether can connect to the protected area, water/lava/fire can spread from outside into the protected area, and pistons can push items inside as well. Players can place blocks on the edge of the protected area if placed against the side of a block on the outside of the area. However, if the edges of the protected area are avoided, small, indestructible structures can be built. Paintings that are put up can be removed by players in the safe zone.

Animal spawning
Approximately one in ten newly generated chunks will contain mobs, usually in packs of up to four of the same species. They will always spawn on the highest available block in a column i.e. the one that can see the sky. For an animal to spawn on it, this block must be opaque and the two blocks above it must be transparent. The block does not need to be grass nor does it need to be illuminated (as it does with Mob Spawning).

Animals do not spawn in desert or ocean biomes, with the exception of squid.

Randomness for animal spawning is derived from the world seed, which means that worlds with the same seed will generate chunks with the same animals in the same places.

Very rarely, new animals can spawn in already generated chunks, just like monsters do. When animals spawn in this way, they do so only on grass blocks with light level 9 or greater above them. This is also a requirement for animals spawning from monster spawners. Unlike monsters, animals do not spontaneously despawn, except for wild ocelots and wolves (which can despawn only when they are hostile).

Mob spawning
Mobs are broadly divided into four categories: hostile, friendly, water (i.e. Squid) and ambient (i.e. Bat). Hostile mobs have a spawning cycle once every game tick (1/20th of a second). Friendly and water mobs have only one spawning cycle every 400 ticks (20 seconds). Because of this, hostile mobs can spawn at any time, but animals spawn very rarely. Instead, most animals spawn within chunks when they are generated.

Mobs spawn naturally within a 15x15 chunk (240x240 block) area around the player. When there are multiple players, mobs can spawn within this distance of any of them. However, mobs that move farther than 128 blocks from any player will immediately despawn (see Despawning), so the mob spawning area is effectively limited to spheres with a radius of 128 blocks, centered at each player.

Mob caps are directly proportional to the total number of chunks eligible for spawning. To calculate the cap, the spawning area is expanded by one chunk in every direction, so that it is 17x17 chunks in size, and then the total number of chunks is plugged into the following formula:

cap = constant * chunks / 256

Each mob category has a separate cap and a different constant in the formula:

Hostile = 70 Passive = 10 Ambient (Bats) = 15 Water = 5

In single player mode, the chunk count is 17x17 = 289, and the caps work out to:

Hostile = 79 Passive = 11 Ambient = 16 Water = 5

In multiplayer, chunks that are in range of multiple players are only counted once. So the more spread out the players are, the more chunks will be covered and the higher the caps will be.

The cap is checked once at the beginning of each spawning cycle. If the number of living mobs in a category is over its cap, the entire spawning cycle for that category is skipped.



For each spawning cycle, one attempt is made to spawn a pack of mobs in each eligible chunk. A random location in the chunk is chosen to be the center point of the pack. For the pack to spawn at all, the center block must be water for water mobs and air for all other mobs. Note that in the latter case, it must actually be an air block. Any other block, even a non-colliding one, will prevent the entire pack from spawning.

If the pack location is suitable, 12 attempts are made to spawn up to 4 mobs (8 for Wolves, 1 for Ghasts) within a 41x1x41 area centered at that block (that's a 41x41 square that is one block high). Mobs will spawn with the lowest part of their body inside this area. For each spawn attempt, a block location within the pack area is chosen at random. Though the pack area extends 21 blocks out from the center, the random location is heavily skewed toward the center of the pack. Approximately 85% of spawns will be within 5 blocks of the pack center, and 99% within 10 blocks of the center.

All mobs within a pack are the same species. The species for the entire pack is chosen randomly from those eligible to spawn at the location of the first spawn attempt in the pack:
 * In the Overworld, this depends on the biome:
 * Most biomes can spawn sheep, pigs, chickens, cows, spiders, zombies, skeletons, creepers, Endermen, Slimes (only in certain chunks if not in a swamp), and Squid.
 * Forest and taiga biomes can also spawn Wolves.
 * Jungle biomes can also spawn Ocelots.
 * Desert, beach, river, and ocean biomes cannot spawn animals; only hostile mobs and Squid.
 * Mushroom biomes can spawn only Mooshrooms.
 * There are actually two ways for a Slime to naturally spawn without a Monster Spawner: In any eligible chunk under layer 40, or in a swamp biome at a low light level.
 * Cave spiders spawn only from their specific Mob Spawners, which are found in Abandoned Mine Shafts among many cobwebs.
 * Silverfish spawn from special stone, cobblestone, and stone brick blocks found in strongholds and extreme hills biomes. They also spawn from specific spawners found in strongholds.
 * Blazes spawn from their specific spawners in Nether Fortresses and can also spawn elsewhere in the structures.
 * Wither Skeletons and Skeletons can spawn in Nether Fortresses.
 * The Nether itself can spawn only Ghasts, Zombie Pigmen, and Magma Cubes.
 * The End can spawn only Endermen.
 * The Ender Dragon spawns naturally in The End; but only one, ever; and not as part of the general mob spawning process.
 * Snow Golems, Iron Golems, and Withers only spawn when built with the exception of Iron Golems spawning in villages with 10 villagers and enough houses.

Each individual spawn attempt succeeds only if all of the following conditions are met:


 * There must be no players and no player spawn points within a 24 block distance (spherical) of the spawning block


 * If it's a squid, then...
 * the spawning block must contain liquid (water or lava)
 * the spawning block must be between level 45 and 62, inclusive
 * the spawning mob must not be obstructed by other mobs


 * If it's not a squid, then...
 * the spawning block itself must be non-opaque and non-liquid
 * the block directly below it must be opaque
 * the block directly above it must be non-opaque
 * the spawning mob must not be obstructed by blocks, other mobs, or water


 * If it's an animal, then...
 * the block directly below the spawning block must be grass
 * the light level of the spawning block must be 9 or brighter


 * if it's an ocelot, then...
 * the spawning block must be above level 62
 * the block directly below the spawning block must be grass or leaves
 * there is a 1/3 chance the spawn will fail


 * If it's a hostile mob in the overworld, then...
 * the light level of the spawning block must be 7 or darker, and more light increases the chance that the spawn will fail
 * sunlight falling on the spawning block further increases the chance that the spawn will fail, by up to 50%


 * If it's a Slime, then...
 * the spawning block must be in a chunk eligible to spawn slimes (see the Slime page for details)
 * the spawning block must be below level 40
 * if the spawn is in a swamp biome, the light level just has to be low
 * there is an additional 90% chance the spawn will fail, thus slimes only spawn 1/10th as often as other mobs, all other things being equal


 * If it's a Ghast, then there is a 95% chance the spawn will fail, thus ghasts only spawn 1/20th as often as other mobs

If all of these conditions are met then the mob is spawned. The pack is complete when 4 mobs have spawned (or 8 wolves, or 1 ghast), or 12 attempts have been made, whichever comes first. The exception(s) to these rules is the Enderdragon

Other types of spawning
A Monster Spawner causes mobs to spawn constantly in the area around it.

A thrown chicken egg has a 1 in 8 chance of spawning a chicken, and an additional 1 in 32 chance of spawning 4 chickens from a single egg, so there is a total of 1 in 256 chance for a single thrown egg to spawn 4 chickens.

Cows, chickens, pigs, sheep, mooshrooms, villagers, ocelots and wolves can breed. All of this requires a player to breed them except for villagers.

Two snow blocks in the overworld placed on top of each other, with a pumpkin or Jack 'o' Lantern, causes a Snow Golem to spawn. Likewise, replacing the Snow Blocks with iron blocks (with an extra one on opposite sides of the higher block) will cause an Iron Golem to spawn. Iron Golems can also spawn in villages (though the algorithm that causes this has not yet been determined). Withers can also be spawned by placing blocks.

In Creative, the player can use Spawn Eggs to spawn most mobs.

Siege: Zombies can spawn in villages. This is not natural spawning, as it can happen in mushroom biomes or if is set.

A Monster Egg will spawn a silverfish if broken, or if a nearby silverfish is attacked.

A single Ender Dragon spawns in The End.

Medium and large slimes and magma cubes will spawn more of them, but in a smaller size.

Zombie Pigmen can spawn from nether portals.

Despawning


Monsters (not holding items or wearing armor) and squid (but not animals), including hostile wolves as of 1.1, can cease to exist, or "despawn", under certain conditions:


 * A mob will immediately despawn if ever there is no player within 128 blocks of it. Note that this appears to be a sphere, not a cylinder from map top to bottom.
 * A mob that has had no player within 32 blocks of it for more than 30 seconds has a 1 in 800 chance of despawning on each game tick (1/20th of a second). Therefore, the half-life of monsters not within 32 blocks of a player is 27.73 seconds, after the initial 30 seconds have elapsed.
 * All hostile mobs (including those that are holding items) in a world will despawn if the difficulty is set to peaceful, regardless as to where the player is positioned in the world.

In multiplayer, despawning does not occur while there are no players in the game.

Trivia

 * Sometimes it is possible for the world spawn to be underground or in the ocean.
 * World spawns can even be inside a dungeon. (very rarely)