I run a very small SMP server running Forge 1.12 hosted through MCProHosting. I have a very few mods installed: StorageDrawers, WAILA and JEI.

I built the mob farm in this video.

The spawn rates are REALLY low, only a couple mobs in over 10 minutes. I've done a lot of research but can't find any useful information. I'm looking for advice on how to make this thing work. I've read that for various reasons, mob farms are just much worse on SMP. Here's some useful information:

  • I wait for spawns between 24 and 128 blocks from the spawning areas.
  • I turned the server's render distance to 10. Helped a LITTLE bit.
  • I used the fill command to ensure NO unlit caves are within a 128 block radius
  • The server is on the Hard difficulty
  • The spawn rate is very low even when I'm alone on the server.

Any help is appreciated.



I downloaded the world and tested the trap in single player. To my surprise, it didn't work!! That's kind of good news. That means maybe it's possible to have this work on the server once I figure out what's wrong with it.

  • 1
    Are you sure you have the right distance to the farm? How is the server performance? Does the same happen without mods? Can you download the world and try it on your own PC? – Fabian Röling Oct 11 '17 at 23:17
  • I am sure I'm the right distance from the farm. The server performance is good. I don't know if this happens without mods, but I'm not willing to test that. Soon I plan to copy the world file and try it in single player. I'm sure it will work fine in that case, though. – CrazyPaste Oct 12 '17 at 3:27
  • At what point did you use the fill command? – GoldNugget8 Oct 14 '17 at 18:13
  • I used the full command in the areas surrounding the spawner. After I built the trap. – CrazyPaste Oct 14 '17 at 18:26
  • Is it a flat world? – rappatic Oct 17 '17 at 16:52

I have recreated this spawner on a test world. I initially built it on a spigot server. I played it as single player and also loaded it in a vanilla server. The spawn rates were substantial all 3 ways.

I can't speak to the possibility that your mods could be causing the issue you are facing though.

Note: A few times, the redstone circuits glitched. I had the clock at the top freeze which caused the water to just stay out which killed spawning. I also had the elevator circuit freeze which caused the items to back up into the hoppers and never come up to the surface. In these cases, the circuits had to be manually reset.

To force the mobs to spawn only on the intended platforms, I filled in most caves and lit the surface for 128 blocks in all directions. You said you filled the caves, if you have not lit the surface, I recommend it. Before I lit the surface, the spawn rate was a bit lower.

I took this screenshot when it was running on the vanilla server. As you can see, every time the water turns off, several mobs spawn. To get this picture, I used a hacked client with mobESP and freecam. MobESP highlights the mobs and freecam allowed the screenshot to be taken from underground like this.


View edit below before downloading this version
I uploaded this world to mediafire. It is named Spawner.zip and it is 5.52MB. It can be downloaded here. I recommend you download it and run it temporarily on your server to see if your mods are causing the problem or if it is something else.


I recreated this in an empty world out of glass for a smaller world size and a way to view it. You can see the item stream headed up on the left side of the image.


Download this world here. It is named Spawner2.zip and is 330.13KB. Use this temporarily, just to test if the spawner design will work on your server. To note, the spawner works best at night. Use /time set night when testing as I left the day cycle functioning.

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  • Thank you so much for this detailed response. I will mark this as the correct answer. I don't know why or how. But my spawner started working at some point. I always sleep when waiting for spawns before the light level is low enough for anything to spawn outside. And I don't use the item elevator because it wasn't working too well. – CrazyPaste Oct 19 '17 at 13:10
  • Not a problem. I'm glad it started working. What was happening with the item elevator? Now I am modifying the design to be an XP farm. Quite the chore though. Separating the mobs is always a process. – IronAnvil Oct 19 '17 at 14:50
  • I didn't fix the item elevator. I couldn't get that part working. I just put a chests at the end of the hopper chain. It's annoying having to go way down there to collect, but I don't mind. But at least the main part of the farm is working. – CrazyPaste Oct 19 '17 at 18:23
  • Do you have a discord name or a server IP? I can come take a look, see about getting that elevator working. – IronAnvil Oct 19 '17 at 19:37
  • Thank you, that's nice of you. But it's alright. I'll fix it later. :) – CrazyPaste Oct 19 '17 at 19:45

I think I know what you're problem is. You used the fill command to fill caves, but you also filled the mob farm, even just a little bit, and now less things are spawning.

Also, I never saw you put water down. If you did than it's not a problem, but if you didn't it might help.

Also, another player may be stealing your spawns. Make sure nobody else has a mob farm nearby.

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  • Thank you for the answer. I only test this when I'm alone on the server. We've built other mob traps but they are 500+ blocks away. (And the other traps didn't work anyway) lol And, I definitely did not accidentally fill in any of the mob trap. I was very strategic in the way I filled in everything around the trap. – CrazyPaste Oct 14 '17 at 18:27

There are lots of things that Minecraft checks for before spawning mobs. Hostile mobs, however, really only need two requirements:

  • If a mob spawns, the block that it is standing on must be opaque (solid, like stone or grass) and the two blocks above it must be transparent, like glass or leaves. Air will count as a transparent block.
  • The light level of the block must be seven or lower (unless a thunderstorm is happening). Sunlight falling on the block will decrease the chances of the mob spawning by up to 50%.

Make sure both these points are met, or else your mobs will not spawn. Also, try to be withing 32 blocks of the mob farm, because mobs will be guranteed to spawn. Anything past that can be risky.

If there's a mob with no player within 32 blocks of it, the mob will despawn in about a minute.

In addition, here's some tips:

  • Build a village, so large packs of zombies may be able to spawn.
  • Make the area the mobs can spawn in as dark as possible.
  • Spiders can spawn in mob farms and block 1x1 wide channels. In other words, place barriers to create 2x2 squares to minimize the chances of them spawning.

I hope this solved your problem. If not, it's probably the fault of the server. The server.properties file should have these values set:

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