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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →No—moon phase does not affect slime chunks. Slimes in designated underground slime chunks can spawn below Y=40 at any light level, whether the moon is full, new or anywhere between. Lunar brightness matters only for the separate surface-spawning mechanic in swamps and mangrove swamps.
The short answer: slime chunks ignore the moon
A slime-chunk farm does not become more or less productive because of the lunar phase. In a valid slime chunk, slimes spawn below Y=40 without a moon-based restriction and without a light-level requirement. A full moon cannot boost that farm, and a new moon cannot shut it down.
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This distinction matters because Minecraft has two different slime-spawning routes that players often combine in one question. Underground spawning uses the world’s slime-chunk data. Surface spawning in swamps and mangrove swamps follows different height, light and moon rules. If you are standing in a swamp waiting for slimes, the moon matters. If you are clearing platforms in a slime chunk, it does not.
How the two slime-spawning routes differ
| Mechanic | Slime chunk | Swamp or mangrove swamp |
|---|---|---|
| Typical spawning height | Below Y=40 | Y=51–69 |
| Light requirement | Any light level | Light level 7 or lower |
| Moon-phase effect | No effect stated | Chance changes with moon brightness |
| New moon | No moon-based restriction stated | Swamp slimes do not spawn |
| Must the area be a slime chunk? | Yes | No |
The comparison reflects the mechanics described by the Minecraft Wiki search material and a third-party guide updated October 2, 2026. That guide says its Java and Bedrock coverage reaches version 26.3, but it is unofficial and not associated with Mojang. Treat version-specific behavior accordingly if you play a different release.
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What happens underground in a slime chunk
Below Y=40 is the relevant height
For the chunk-based route, the spawning area must be below Y=40. Building a room, tunnel or platform above that level does not satisfy the stated height condition, even if the chunk itself is correctly selected. When diagnosing a farm, check the platform’s actual Y coordinate rather than relying on the surface elevation or the position of the chunk border.
Light does not block chunk-based slimes
Slime chunks do not have a light-level requirement in the cited guide. You may illuminate platforms, walkways and nearby caves for visibility and safety without preventing slime spawns on those platforms. Lighting is therefore a safety and mob-control choice, not a lunar substitute or a condition that the moon changes.
The chunk must actually be designated for your world
Not every chunk can produce slimes through this route. You need a chunk that the game’s generation rules designate as a slime chunk. A finder must use the correct edition: the guide describes Java slime chunks as depending on the world seed and chunk coordinates, while Bedrock chunk selection depends on chunk position alone. Select the Java or Bedrock mode that matches your world before trusting the displayed coordinates.
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When the moon really does matter: swamp spawning
Surface slimes use a different rule set
Slimes can also appear naturally in swamps and mangrove swamps between Y=51 and Y=69 when the light level is 7 or lower. This route does not require a slime chunk, so a swamp can produce slimes even when its chunks are not designated for underground slime spawning.
Full moon versus new moon
The cited references describe swamp slimes as most numerous during a full moon. They also state that swamp slimes do not spawn during a new moon. Other lunar phases fall between those extremes, with the chance varying with moon brightness. These statements apply to the swamp route only; they do not alter the below-Y=40 rule in a slime chunk.
Why a swamp hunt can give the wrong impression
If you hunt on the surface during a new moon and find no slimes, it is reasonable to suspect the moon. That observation does not prove that an underground farm is affected. Conversely, seeing good results in a swamp on a full moon does not mean a nearby slime-chunk farm needs the same timing. Identify the spawning route before changing your build or waiting for another night.
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Do slime farms work during a full moon?
Yes. A correctly located underground farm can operate during a full moon, and its chunk-based slime spawning is not improved by that phase. The same answer applies to a new moon: the moon does not impose a chunk-based pause. If production changes from one session to another, investigate the farm’s conditions rather than scheduling work around the lunar cycle.
For a surface swamp farm or a manual swamp hunt, the answer is different. A full moon is the most favorable phase described for that route, while no swamp slimes are expected during a new moon. The two answers are not contradictory; they refer to different spawning mechanics.
What to check when an underground farm is slow
Moon phase is not a useful fix for a low spawn rate in a slime chunk. Check the following causes in order:
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- Confirm the edition. Make sure the chunk finder and its result match Java or Bedrock. The guide describes different inputs for chunk selection, so an edition mismatch can send you to the wrong location.
- Verify the chunk coordinates. Recheck the world seed or chunk position used by the finder and confirm that the farm occupies the designated chunk rather than an adjacent one.
- Measure the height. Confirm that the spawning floor is below Y=40. A room that looks underground may still be too high for the chunk-based rule.
- Inspect the open space. Slimes need enough unobstructed room to spawn. Low ceilings, blocks, decorative details or cramped platforms can reduce usable spawning area even when the chunk and height are correct.
- Check the difficulty. The guide identifies Peaceful difficulty as a constraint. If the world is set to Peaceful, hostile-mob spawning behavior can prevent the expected result; test on a non-Peaceful difficulty appropriate to your world.
- Check player distance. Your position affects whether mobs can spawn and remain active. If you stand too close or too far from the platforms, the farm may not operate as intended. Use the game’s normal spawning-distance rules when choosing an AFK or waiting position.
- Reduce competing mobs. Nearby caves and dark spaces can consume available hostile-mob spawning opportunities. Lighting or otherwise managing those areas can improve the share of spawning attempts available to slimes.
- Allow enough time for observation. A short wait is not proof that the chunk is invalid. Watch from a suitable position after confirming the structural and world settings above.
Lighting your platforms is not on this list as a failure cause because the cited chunk rule allows any light level. Use lights for safety and to make surrounding-mob management easier.
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Before you build
- Record whether the world is Java or Bedrock.
- Use a chunk finder configured for that edition.
- Confirm the displayed location against your in-game coordinates.
- Plan the spawning platforms below Y=40.
After the platforms are built
- Stand on or near the planned waiting location and read the current coordinates.
- Confirm that every intended spawning floor remains below Y=40 after adding slabs, water channels or collection spaces.
- Remove blocks that leave too little open room for a slime to appear.
- Add lighting where you need visibility; it will not disqualify the platforms under the stated slime-chunk rule.
- Inspect nearby caves and other dark areas for competing mobs and light or manage them where practical.
- Test on a non-Peaceful difficulty, remain at a suitable distance, and observe the farm without using the moon phase as a variable.
This sequence separates errors in chunk selection, height, space, difficulty, distance and mob competition. Changing the lunar phase changes none of those checks.
Common misconceptions
“A new moon stops all slimes.”
It stops swamp slimes according to the cited references, not slimes in designated underground chunks. The word “all” combines two separate systems and leads to the wrong diagnosis for a farm below Y=40.
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“A full moon makes every slime farm better.”
A full moon is associated with the highest swamp-spawning chance described in the references. It is not a boost for the chunk-based route, which has no stated moon-phase modifier.
“I must keep a slime-chunk farm completely dark.”
The underground rule is described as working at any light level. Darkness may be useful for some other hostile-mob mechanics, but it is not required for slime spawning in the slime chunk described here.
“A swamp and a slime chunk are the same thing.”
They are not. A swamp is a biome-based surface route with Y=51–69, light level 7 or lower and moon-dependent chances. A slime chunk is a chunk-based underground route below Y=40 that does not use the moon phase as a condition.
Edition and version caveats
Finding the correct chunk is edition-sensitive. The cited guide says Java selection depends on the world seed and chunk coordinates, whereas Bedrock selection depends on chunk position alone. Do not copy coordinates from a finder configured for the other edition.
The same guide, updated October 2, 2026, says its Java and Bedrock coverage reaches version 26.3. The available references do not establish that every future or older release behaves identically, and no official Mojang or Microsoft page was identified for this explanation. If your version differs, verify the finder’s stated compatibility and treat unexpected behavior as a possible version issue rather than evidence that the moon controls slime chunks.
Bottom line for builders and swamp hunters
Use the moon as a planning factor only when you are hunting or farming slimes in a swamp or mangrove swamp: full moon is the most favorable phase described, and new moon produces no swamp slimes. For an underground slime-chunk farm, ignore the lunar calendar. Put the spawning area below Y=40 in the correct designated chunk, provide sufficient open space, use a non-Peaceful difficulty, stand at an appropriate distance and manage competing mobs. Those conditions—not the moon—determine whether the chunk-based farm works.
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