Why Is My Farm Not Working?

The full list, in the order worth checking

Farms fail for a small number of reasons, and the order you check them in matters more than the list itself. Most people start by rebuilding the redstone, when the actual cause is usually something that takes ten seconds to rule out.

Mob and XP farms

1. You are standing too close. Hostile mobs never spawn within 24 blocks of the player. If the AFK spot is closer than that to the spawning floor, the farm is off while you are standing there. This is the most common cause of a completely dead mob farm and the cheapest to check: press F3 and compare coordinates.
2. Light is leaking in. Hostile mobs need light level 0. One transparent block or an unsealed corner raises the light across several floor tiles. Check the floor with F3 in daylight, in several spots rather than just the middle.
3. The chunk is not ticking. Blocks and mobs update only inside simulation distance, which is a separate setting from render distance. You can watch a farm that is not running. See render vs simulation distance.
4. Something else is eating the mob cap. The hostile cap is shared across everything loaded. Unlit caves near the farm fill it with mobs you never see. A mob switch suppresses spawns elsewhere so your farm claims the whole cap.
5. The fall is wrong. Under about 22 blocks, mobs survive with too much health for a one-hit kill. Past 23 to 24, they die on impact and you get no experience and no player-kill drops. Water in the shaft resets fall damage, so only the final air gap counts.
6. The drops are being destroyed or stranded. Lava that touches item entities burns them, and items only enter a hopper from directly above it. Drop something by hand on the collection floor and watch whether it reaches the chest.

Iron farms

1. It is not a village yet. Golem spawning needs at least three villagers that have each claimed a bed. Placing a bed nearby does nothing; the villager has to path to it and link. A linked villager walks to its bed at night.
2. The zombie trigger broke. Golems appear because villagers are frightened by a zombie they can see. If it despawned or lost line of sight, spawning stops. Name-tag the zombie and keep it visible behind glass.
3. Golems spawn outside the platform. The village boundary includes any valid ground nearby, not just the platform you built.
4. The iron is burning. Lava touching the item path destroys the ingots. Separate the kill mechanism from where the drops fall.

Crop and plant farms

1. The stem has nowhere to fruit. Melon and pumpkin stems need a free, valid block beside them to grow fruit onto. With every adjacent tile occupied, the stem matures and then produces nothing, while looking perfectly healthy. See the melon and pumpkin guide.
2. Not enough light. Most crops need light level 9 or above to advance a growth stage. Nether wart is the exception: it needs no light at all, and bone meal does nothing to it.
3. The farmland dried out. Farmland stays hydrated within 4 blocks of water. Beyond that it reverts to dirt and the crop pops off.
4. Something broke the plant. Flowing water breaks crops at any stage, jumping on farmland reverts it, and a cactus breaks when any solid block sits horizontally adjacent to it, including another cactus. See the cactus farm guide for how farms use that rule deliberately.
5. It is growing, just unevenly. Crops advance on random ticks rather than a timer, so a plot can sit still for minutes and then jump several stages. More tiles smooths it out.

Frequently asked questions

Why is my mob farm not spawning anything?

In most cases the AFK spot is within 24 blocks of the spawning floor, which switches spawning off entirely. After that, check for light leaks, then whether the chunk is inside simulation distance.

How far away do I need to stand from a mob farm?

At least 24 blocks from every spawning floor, measured in a straight line through all three axes, so a floor directly above you counts its vertical distance. 25 to 30 blocks gives you a margin.

Why does my farm only work when I am standing next to it?

The chunk falls outside simulation distance when you leave, so nothing ticks. Raise simulation distance, build in the spawn chunks, or use a chunk loader.

Why does my melon farm produce nothing even though the stems are grown?

The stems have no free adjacent block to grow fruit onto. A mature stem with nowhere to fruit looks identical to a healthy one, so check the tiles beside it rather than the plant.

For the builds themselves, the farm guides collection covers every farm with a working design, and the mob spawner optimizer works out AFK placement and spawnable area for a specific build.