Fence – Minecraft Wiki – Wikia

Fences are Wood blocks that are partially transparent, and they have a 1.5 block tall hitbox, meaning that they cannot be jumped over by a player or mob, unless the mob is a horse, has jump boost, or is standing on a Slab. They were added in the Secret Friday update. Fences are found in NPC Villages, where they act as small enclosures around some of the houses, on roofs of some houses, pillars for wells, lamp-posts with a block of black Wool placed on it, or in houses with a wooden Pressure Plate placed on top of it, forming a table-like structure. They are a wooden pole when there is no block on any side, but they connect to any adjacent blocks, extending the hitbox horizontally. A gate can be used to continue the look of a fence while allowing access to the other side to players.

A fence's primary use is enclosing an area. It functionally serves to keep mobs (usually animals) and players either inside or outside. This is because fences are 1.5 blocks tall to players and mobs, although they appear to be only 1 block tall, and are only that tall to other blocks. A wide area can be made monster-resistant by enclosing it in fences and lighting the inside portion heavily. This keeps any monsters from spawning within the fence, and keeps most monsters which spawned outside the fence from coming in. A notable exception is spiders, which can climb over it, althoughthis can be avoided by putting a normalblock on top of a two block tall fence, as it will hit the bottom of the block and fall down when climbing. In addition, while skeletons are unable to cross a fence, they can shoot over it. Torches can also be placed on top of fences, creating a safe perimeter. Chickens can go close enough to fences to stand entirely on the block the fence is on, allowing it to fall down and escape if said block is air.

Fences can also be used as railings, especially on the edges of balconies or floating platforms. Since fences cannot be jumped over accidentally, this keeps players and mobs from falling off while still allowing them to easily see past the fence. Fences can be used as an anchor for animals if they are attached to a Lead.

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Fence - Minecraft Wiki - Wikia