Netherite Finder

Two passes run per chunk, both seeded from the chunk's coordinates. The first ("large") pass scatters debris from Y=8 to Y=22 with peak density around Y=15. The second ("small") pass scatters from Y=8 to Y=119 with much sparser placement. Roughly three-quarters of all ancient debris ends up in the large-pass range.

Within those ranges, debris generates as clusters of 1-3 connected blocks. The map shows each cluster's origin with a small ×N badge for the block count. Clusters near caves, lava, or open air get partially culled at generation time, which is why occasional clusters appear smaller in-game than the map predicts.

Both editions use the same two-pass system at the same Y-ranges. The difference is in the random number generators feeding the placement math.

Java uses Xoroshiro128++ (since 1.18), seeded from the world seed plus chunk coordinates. Bedrock uses a 32-bit MT19937 with a different chunk-seed derivation: worldSeed XOR (chunkX·r1 + chunkZ·r2), where r1 and r2 come from two outputs of the world-seed-initialized MT.

Practically: identical world seeds in Java vs Bedrock produce different debris layouts. Same edition, same seed, same chunk coordinates always produces the same layout. Seed compatibility across editions doesn't extend to ore placement, or to terrain, or to structures, for that matter.

Y=15 is the conventional answer and it's mostly right. The nuance:

• Y=14 vs Y=15 vs Y=16: density is nearly identical. Y=15 edges the others by a margin too small to matter in practice.
• Bed mining: beds explode with a fixed radius, so the difference between Y=14 and Y=15 is irrelevant. Both reveal roughly the same Y=12 through Y=18 band.
• TNT tunneling: vertical reach is smaller, so Y=15 with 1-block-tall tunnels hits the densest line.
• Below Y=8 or above Y=22: large-pass debris stops entirely. Anything above Y=22 is from the much-sparser small pass, at roughly a quarter of the density.

The map's default y=5 to y=25 filter covers the large-pass range plus a small buffer. Adjust via Advanced... if you're after something specific.

Ancient debris uses an air-exposure cull: when world generation tries to place a block, if the target position is air, lava, or any non-replaceable block, the placement is skipped silently. The map's debris icons are computed from the seed's RNG alone; they're the positions the algorithm would place, before the terrain check runs.

This means an icon on the map can fail to produce debris in-game for two distinct reasons:

• Lava overlap. If the target position is inside a lava lake, the placement is skipped entirely. An icon sitting in the middle of an orange lava region on the map will essentially never have debris there in-game. The bigger and deeper the lava lake, the more likely the icons over it are false positives.
• Air exposure (caves, ravines, fortresses). Cave carvers run after debris placement and can hollow out a position that was solid netherrack at generation time. Cave-pocket lava (the small pools you find while mining) is generated by carvers too. This map doesn't model carvers, so icons near hidden caves can also be false positives.

Clusters of ×2 or ×3 walk to face-adjacent neighbors before placing each block, and each block in the cluster faces this check independently. A cluster the map shows as ×3 might land in-game as ×2 or ×1 if some of its blocks end up in air or lava.

Practical guidelines for reading the map:

• Icons inside large visible lava lakes: assume they won't generate. Don't tunnel toward them.
• Icons on the edge of a lava lake: gray zone. The block at the icon's exact Y might be solid netherrack even if the lake covers part of the column above or below it. If the terrain map at Y=15 reads solid (dark color) at the icon position, the debris is probably real.
• Icons in dense netherrack, away from visible lava: trust the icon. Within-cluster count overestimation is the dominant error here, not "no debris at all."

This is also why a single screenshot from an in-game test doesn't always agree with the map: the in-game game is showing post-cull reality, the map is showing pre-cull spawn positions. The right validation is to check whether the visible debris in-game lines up with the map's icons, not whether every map icon has visible debris.

Mostly no. Ancient debris generation does not check biome. It places based on chunk coordinates and noise functions, independent of whether you're in Nether Wastes, Crimson Forest, Warped Forest, Soul Sand Valley, or Basalt Deltas.

The reason it feels like biomes matter: basalt deltas have more visible lava lakes (eating into mineable space), soul sand valleys have more cave openings (causing air-exposure culling), and crimson/warped forests have denser overhead terrain (making mining harder). Same debris density, different access difficulty.

If you're picking where to dig from this map, prioritize biomes with continuous netherrack (usually Nether Wastes and Warped Forest) over basalt deltas.

Other tools (orefinder.gg, findores.app, gildedbedrock) output coordinate lists or chunk grids. They'll tell you "debris at X=143, Z=-218" and leave you to figure out whether that block is in a solid wall of netherrack or floating in the middle of a lava lake.

This tool overlays debris on the actual Nether terrain at Y=15. Lava lakes appear orange, navigable netherrack appears dark, biomes are color-coded. You can see at a glance whether a cluster is mineable or buried under forty blocks of lava.

The terrain layer uses the cubiomes library (Cubitect's original for Java, Reed Cartwright's fork for Bedrock). The debris layer uses the algorithm above, validated against ground truth across 16 world seeds and 356+ confirmed positions.

A few things people repeat that aren't quite right:

• "Ancient debris only spawns near lava." Not true. Debris generation runs across the full Y range independent of lava. Lava lakes just happen to occupy the same Y-band as the densest debris, so the correlation feels causal.
• "Bed-mining at Y=12 is best." It works, but Y=14-15 with beds covers the densest part of the large-pass range. Y=12 catches the lower edge and misses everything above Y=15.
• "Higher Y means more debris." Above Y=22 only the small pass generates, at roughly a quarter of the density of the large-pass band.
• "Same seed gives the same world in Java and Bedrock." No. Different RNG, different chunk-seed math. Terrain, structures, and ore placement all diverge.