Dungeons and mob spawners
How monster-room attempts are chosen
Java 26.3 places the monster_room feature through two placed features. The upper pass makes 10 attempts per chunk from Y=0 through the top generation level. The deep pass makes 4 attempts from 6 blocks above the world bottom through Y=-1. For the default Overworld height, these ranges are Y=0-319 and Y=-58 through -1.
Fourteen attempts do not mean fourteen rooms. The game checks the blocks surrounding each chosen position, including the floor, ceiling and openings, before constructing the room. Many attempts fail. This is why a list of random positions is not enough to locate actual spawners.
How to find a dungeon
- 01
Select Java, the seed and the matching supported version. Enable the dungeon layer and zoom in so the finder can examine the visible chunks.
- 02
Open a marker to read X, Y and Z. Keep the Y value with the horizontal coordinates; the room can be far below the surface directly above it.
- 03
Use the candidate to narrow a cave search or inspect that position in a Creative copy. A missing room can reflect a terrain check that the map only approximates.
Spawner weights
The Java 26.3 monster-room mob list contains Skeleton once, Zombie twice and Spider once. Uniform selection from those four entries gives 25% skeleton, 50% zombie and 25% spider. Those are the room-generation weights, not the current population around a spawner. Changing difficulty, blocking the spawn area or changing the spawner later does not alter where the original generation attempt was made.
Why a candidate can fail
The room needs a suitable solid floor and ceiling and an allowed number of wall openings. The map reproduces the candidate random sequence and applies a cave-noise filter, but it does not reconstruct all aquifer water and legacy cave carving. Those missing block details can change whether construction succeeds. The mob label also depends on the room-construction random sequence, so it is an estimate where the surrounding block reconstruction differs.
Worked example: a deep spawner
Enter seed 4698007340012694373 in Java 26.2 and look at X=-277, Y=-8, Z=-106. The map shows a dungeon candidate there. The repository engine tests record that coordinate from a real vanilla save and check that it survives the map terrain filter. This is an engine-test example, rather than a /locate result: monster rooms are features and are not located by the structure command.
Use the height, not only the icon
At Y=-8, the example belongs to the deep pass, below the Y=0 split. Copying only X and Z would leave a large vertical search. A surface biome at those coordinates does not tell you whether the room is flooded or connected to a traversable cave. The finder also does not count nearby spawners as a working multi-spawner farm: that requires checking the actual rooms and player activation position together. Bedrock monster rooms are outside this Java finder.
Dungeon Finder FAQ
Can /locate structure find a monster room?
No. The example is backed by a generated-save engine regression, because monster rooms are placed features.
Do ten upper attempts guarantee a spawner?
No. Room construction can reject an attempt after checking the surrounding blocks.
Does the marker include a reliable mob label?
The map estimates the mob from construction randomness; differing room surroundings can change that prediction.
Related spawner tools
Other finders
Map and coordinate reports
For a missing or misplaced result, include the full seed, Java or Bedrock, game version, dimension, coordinates, and what appeared in the world. Mention mods, datapacks, add-ons, experiments, server software, or old chunks when relevant.
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