Enter your seed and pick your edition. Every green square is a slime chunk: a 16 x 16 column where slimes spawn underground below Y=40, whatever the biome or light level.
Click or tap any chunk for its chunk coordinates and exact block range. The panel also tells you whether the chunk at the center of the map is a slime chunk, so you can fly to your base with Go to and check it instantly.
Java slime chunks come from your world seed, so every seed has its own pattern.
Bedrock slime chunks ignore the seed entirely: every Bedrock world has them in the same places. The seed still matters for the terrain you see underneath.
Java slime chunks are computed with the game's own formula and were checked chunk for chunk against Java's real random number generator. Bedrock uses the community-documented formula (a Mersenne Twister seeded from the chunk coordinates).
The terrain underneath comes from the same engine as the Diamond Finder.
Reference: Slime Chunks
Slime chunks are the reason slime farms work. About one chunk in ten is a slime chunk, and which ones they are is decided the moment the world is created, so you can find them by coordinates instead of wandering caves waiting for a slime to appear.
What is a slime chunk?
A slime chunk is a 16 x 16 column of the world where slimes can spawn underground regardless of biome or light level. Roughly 10% of chunks qualify. Chunks line up with coordinates that are multiples of 16, which is why a chunk grid matters when you plan a farm: the spawning area has to sit inside the chunk's edges.
Java vs Bedrock slime chunks
On Java Edition, whether a chunk is a slime chunk depends on the world seed together with the chunk's coordinates, so two worlds with different seeds have different slime chunks.
On Bedrock Edition the calculation uses only the chunk's coordinates. The seed is never involved, so every Bedrock world, on every device, has slime chunks in exactly the same places. Switch the edition on the map to see the right pattern.
Where and when slimes spawn
In slime chunks, slimes spawn below Y=40 on both editions, and light level does not matter. They need a solid block to spawn on and enough room for their size.
Separately, slimes can spawn at the surface in swamps and mangrove swamps at night, depending on the moon phase. That is unrelated to slime chunks, which is why you sometimes see slimes where this map shows none.
Building a slime farm
Look for a slime chunk, ideally two or more touching ones, near where you play. Dig out the area below Y=40 inside the chunk edges and build several layers of flat spawning platforms, at least 3 blocks apart vertically.
Mobs only spawn within 128 blocks of a player and not closer than 24, so you need to stand within that range for the farm to run. Lighting up or filling in nearby caves stops other mobs from using up the spawn cap.