I made a simple mob farm on skyfactory 3 and when I went to check the avaiable mob spawning areas using the F7 key these red crosses came up This means mobs should be able to spawn but they don't. I'm often AFK over 24 blocks away from my farm but still no spawns. Red crosses

Why is my mob farm not working? Anyone knows better mob farm designs for a starting player for skyfactory that maybe do work?

  • 1
    Possible duplicate of What are these red lasers?
    – GiantTree
    Mar 26, 2017 at 15:57
  • allright I will change it to specify around the mobs not spawning...
    – BRHSM
    Mar 26, 2017 at 16:00
  • Make sure you are at least 24 blocks away from where you want the mobs to spawn.
    – GiantTree
    Mar 26, 2017 at 16:01
  • Now it should no longer be a duplicate?
    – BRHSM
    Mar 26, 2017 at 16:02
  • 2
    Definitely not a dupe of the linked question. The linked question is asking what the red lines are, this is asking why mobs aren't spawning on the red lines like they should.
    – MBraedley
    Mar 26, 2017 at 19:20

3 Answers 3


Is that half block under those red crosses? If so, half block does not work for spawning. Quick search only, try this link: http://www.minecraftforum.net/forums/archive/alpha/alpha-survival-single-player/820173-mob-spawning-science?page=1

If that is a full block, follow the answer from @TrueDakkon and add a space above and beside the red crosses. (Sample: Move the top part at least 1 block then add another block on the side of those crosses. You will now have 3 wide 3 height. Try it from there)

P.S. I don't have setup now and I cannot verify my answer. I will try to verify as soon as I got my hands on a Skyfactory setup.

  • I'll check in a few days... have to study too :(
    – BRHSM
    Mar 27, 2017 at 17:23
  • would be cool if you could check this design
    – BRHSM
    Mar 27, 2017 at 17:23
  • Sorry. Been busy with work for the past weeks. Did you fix this already?
    – waaaw
    Apr 6, 2017 at 11:15
  • i am working on it too. i've been busy with school haha
    – BRHSM
    Apr 9, 2017 at 11:06

I don't know what the problem really was but I found the fix for it in that I made a 23 block fall with a spawning room above! enter image description here

using trapdoors I lure down the mobs and they fall to 1 heart so I can kill them easely!

  • I just saw this question got 10k views so for anyone wondering why this is in the future, mobs don't spawn unless they are at least 24 blocks away from the player, which my old setup was not.
    – BRHSM
    Jul 25, 2023 at 10:59

It could most likely be an issue with there just not being enough spawning space. It doesn't look like you have much room, which could mean that the rate at which they spawn will be decreased majorly. Also, make sure that you don't have any gamerule set to keep mob spawning off and that you are in at least easy mode. Overall though, just try and make the spawning platform bigger and give it a bit of time. Also, you want to be at least 24 blocks away from your farm. Over that and mobs will start to despawn randomly. At 128 blocks away, they will despawn instantly.

  • It's the only space in the entire map where they can spawn. The rest is all lit up well. This is so wierd.
    – BRHSM
    Mar 26, 2017 at 19:53
  • Again, try and increase the size of the spawn platform/area they can spawn on. They can't spawn on half slab so you need to either use upside down half slabs or full blocks. There is a huge area in the middle where nothing can spawn. Please refer to this for further information on spawning. minecraft.gamepedia.com/Spawn
    – TrueDakkon
    Mar 26, 2017 at 21:17

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