Minecraft Server Guide

Mob spawning algorithms are some of the more complex background processes in Minecraft. It's incredibly obtuse and unknowable without diving into the code, but once you do, you'll be able to abuse them in a way that will greatly accelerate your resource gathering.

1. The Basics

Mobs are divided into four categories. Hostile, Friendly, Water, and ambient. Out of all these, hostile mobs have the fastest spawning cycle, having a chance to spawn twenty times per second. Friendly and water mobs have only one cycle every twenty seconds. Because of this, hostiles will spawn frequently in in any spawn eligible areas, but passive or friendly mobs rarely spawn. Most animals will spawn in with the world as it generates.

Mobs spawn naturally within a square group of chunks centered on the player. A chunk is the 16x16 area you're in. If you're playing the Java version of the game, you'll be able to see chunks by holding down F3 and G. When there are multiple players (like in a server) then mobs have a chance of spawning around all players. Any hostile mobs that move further than 128 blocks from the nearest player despawn instantly, so if you want enemies to spawn here you, then don't go beyond 128 blocks in a  sphere.

There are also mob caps that limit how many enemies can spawn in a certain area. That's how the game keeps performance up. There are a lot of complicated formulas behind the mob cap, but that isn't too important for our purposes unless you want super optimized farms.

For every 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 able to be spawned on. If the pack location is suitable then up to 12 attempts are made to spawn a pack.

Also, note that mobs cannot spawn within 24 blocks of players - that makes sure that an enemy can just appear behind you and hit you. There are also a few blocks that cannot be spawned on.

• Glass. It isn't an opaque block, and it's transparent.
• A slab on the lower half of a block.
• Carpet.
• Another mob.
• Air.

One last note - hostile mobs in the overworld only spawn if the light levels are below 7. If you're playing java edition, you can check light levels by opening the debug menu with F3.

One last thing to note is that every mob needs vertical space to spawn, but each have different requirements. For instance, creepers can spawn in a 1.5 vertical block space, but zombies and skeletons cannot. Spiders only need 1 vertical block space to spawn, but also needs a 4x4 horizontal space to spawn. You can use this information to your advantage if you want only certain mobs to spawn.

One last thing - slimes completely ignore all these rules. They only spawn either in a swamp biome, or in a randomly generated slime chunk below height 40. Light levels don't matter to then.

2. How to apply this information

All of this information is crucial to building a successful farm. For example, here is a slime farm that I built with inspiration from online. I completely neutralized the ability for every other mob to spawn here so only slimes will spawn and give me their resources. I also have a special platform high in the sky directly above this farm, so very few mobs will spawn in other places.Using this, I've gained thousands of slime balls per day. Do note that this is despite me being on a multiplayer server, where my friends slow the spawn rate of slimes down.

You too can also use this information to optimize resource gain! Good luck!