I built an Xp farm a few days ago, its a simple design and does not rely on a spawner. I know the rules about mob spawn and stuff, but it hasn't been working. The drop height is 22 blocks which should leave skeletons at 1/2 heart. But mobs never fall, and when they do it kills them. But that was at 24 block drop, ive moved it down but nothing happens. I need some help and advice from the community. I cant get a screenshot of it posted but if you guys could help me out there too I will post one. Thanks!

It is a 22 block tube, air is 2x2, up top is four 16x16 platforms 2 blocks above 2x8 canals that carry mobs into the tube. It has 2 high walls with slabs on top, and the whole thing is 200 blocks high (it starts from there)

In terms of low spawn rates there is a number of issues you're working against. You can get more info here:
https://forum.craftymynes.com/763-view-distance-and-mob-spawns

A fall distance of 22 blocks should not be killing the mobs. There are a number of possibilities, but one issue might be if the mobs are bobbing up and down in a water stream before falling, they aren't actually at the block height that you think they are at when they start falling.

Thanks! I'll check that out and take this down if it is fixed!

So would it be a great idea to clean out a chunk (by at least reducing surface for mobs to spawn) where the spawner is? could i leave the chunk alone and just light the whole darn thing up well? Where I have it built I am sure it wouldn't be super bad

I only know of one spawnerless overworld grinder that's worked, and that was on 7 view distance without 1.9 lag issues.

If you want a good test to see if your idea will work. Open a single player world set the the render distance to 4. Quickly mockup the most basic version using /fill and /clone. If it works theres a good chance it will work on the server.

A lot of spawnerless mob farm designs just don't work well. This is something that it really is worth testing in singleplayer first. In general if the design relies on mobs moving themselves it's going to end badly. You need some system that moves the mobs to the drop shaft.

What do you mean? I dont know those commands (xD noob)

As pand1024 and I both mentioned in the thread he refers to above, any overworld spawnerless grinder on this server will have a very poor drop rate unless it is incredibly large. Honestly it's something of a lost cause in my opinion, particularly if you want to use it for xp.

If you want a grinder for xp, try a baze spawner or enderman farm. Dual cave spider spawners are also great and fairly easy to find using subtitles.

Regarding the drop distance, watch out for mobs with armour on. Skellies and zombies can have feather falling so they won't die from a 24 block fall.

Overworld grinders are just a nightmare in general when you have the view distance locked at 6.

What about the rule that mobs over 100 and something (idk) will auto despawn, it is 200 blocks y....

baronbattlebread told me you're not gonna get that kind of spawner working unless the server is practically empty, you're competing for spawnability with the whole server, i built the exact same grinder as you in the 1.8 server and found no entities were even spawning, i'd be lucky for 1, are you having the same problem? this may be able to be solved by building a much bigger mob grinder at the same height and the mobs don't have to move, look up mumbo jumbo and build that one, you might have more success but it's still gonna be ridiculously slow

@TheMightyDrex What about the rule that mobs over 100 and something (idk) will auto despawn, it is 200 blocks y....

No. This is not correct. Go reread : (

Ok. Now i know thanks panda and nut, i actually built my house on a mineshaft coincidentally, so making one shouldnt be a problem.