Slimeballs gate sticky pistons, leads and slime blocks, and the usual way players hunt them — dig out a big room below Y=40 and hope — fails far more often than it works. Slimes do not spawn anywhere underground. They spawn in specific chunks, decided by your seed.
What a slime chunk actually is
Roughly one chunk in ten is flagged as a slime chunk. The flag comes from the world seed and the chunk coordinates run through a fixed calculation, so it is decided the moment the world is created and never changes.
Inside a slime chunk, slimes spawn below Y=40 in any light level. Outside one they will not spawn underground at all, no matter how large or well-lit your room is. That is why "I dug a huge cave and got nothing" is the normal outcome rather than bad luck.
The swamp exception
There is a second way to get slimes that has nothing to do with chunks: swamps. Slimes spawn in swamp biomes between Y=51 and Y=69 at night, in low light, and they care about the moon phase — full moon is best, new moon produces none.
If you just need a few slimeballs tonight, a swamp at full moon beats building anything. For a steady supply you want a chunk-based farm.
Finding your slime chunks without digging
Because the flag is derived from the seed, you can look it up instead of prospecting. Enter your seed, overlay the slime-chunk grid, and every qualifying chunk is marked.
Pick one that is convenient rather than the nearest: a slime chunk under an ocean or already near your base saves far more time than a slightly closer one under a mountain.
- Get the seed with /seed in-game
- Match the edition — Java and Bedrock compute slime chunks differently, so the overlays are not interchangeable
- Line the chunk grid up in-game with F3+G on Java so you dig inside the right 16x16, not one chunk over
Making the farm actually produce
Locating the chunk is half the job. Most farms that "do not work" fail on spawn rules, not on the chunk.
- Clear the full 16x16 from bedrock up to Y=40 — partial rooms cut rates hard
- Light or slab every other cave within 128 blocks, or they compete for the mob cap
- Stay between 24 and 128 blocks away: closer and slimes despawn, further and they never spawn
- Small slimes need a 1-block gap, big ones need 3 — build for the size you want to collect
Find slime chunks in your seed
FAQ
Why are no slimes spawning in my slime chunk?
Usually the spawn rules, not the chunk. Slimes only spawn below Y=40, the room needs to be fully cleared, nearby caves need lighting so they do not eat the mob cap, and you have to be 24 to 128 blocks away.
Can I change which chunks are slime chunks?
No. The flag is derived from the world seed and the chunk coordinates, so it is fixed when the world is created. The only way to get different slime chunks is a different seed.
Do I need a slime chunk to get slimeballs?
No — swamps spawn slimes between Y=51 and Y=69 at night, best at full moon. Quicker for a handful, but a slime-chunk farm is the reliable long-term source.