Monster Spawner generates exclusively in pre-built structures — dungeons (zombie, skeleton, spider), abandoned mineshafts (cave spider), Nether fortresses (blaze, one or two per fortress), strongholds (silverfish, in the end portal room), bastion remnants (magma cube) and woodland mansions (spider, in a rare secret room). The texture is a black metal cage with a tiny rotating mob figure inside, indicating which entity it produces. The device cannot be crafted and cannot be obtained even with Silk Touch — mining always destroys it permanently.

When a player is within sixteen blocks, the device attempts to spawn its mob every ten to forty seconds, up to four mobs per attempt, stopping at a cap of six entities in the immediate area. The spawn requires the same conditions the mob normally needs (light level, space), which is why most XP-grinder farms surround the spawner with darkness and water columns to channel mobs into a kill zone. Mining the block with a pickaxe yields only 15–43 experience, and once destroyed, a spawner cannot be replaced — some servers use commands to change the mob inside, but in vanilla survival the entity is locked at world generation.