World Generation

World generation is how Minecraft turns a seed into terrain: noise decides where blocks are solid, biomes decide what they look like and what spawns on them, features and structures decorate the result. All of it is data-driven, so a datapack can replace any part of it.

Kore maps that data onto Kotlin builders. Everything on these pages produces JSON files under data/<namespace>/, and the whole surface is typed, so Blocks.STONE or Biomes.DESERT are checked at compile time instead of at world load.

Reference: World generation

Pages

How A Chunk Is Built

Every chunk goes through the same ordered steps. A chunk that has not reached the last one is a proto-chunk, invisible to players; once it does, it becomes a level chunk.

This ordering explains most of the behavior you will run into: carvers run before features, which is why a cave never destroys a tree, and structures start before terrain, which is why terrain can adapt around them.

Reference: Generation steps

Decoration Steps

The features step is itself split into 11 decoration steps, run in order. A biome lists its placed features per step, and the structures of a step are placed before the features of that same step.

Reference: Decoration steps

Files Kore Writes

Replace <ns> with your namespace.

A file name containing slashes lands in subfolders, so noise("cave/entrance") writes worldgen/noise/cave/entrance.json.

A Complete Custom Dimension

The smallest set of files producing a playable world of your own: a noise, the density functions shaping it, the noise settings wiring them together, a biome, a dimension type and the dimension itself.

fun DataPack.createCustomWorld() {
	// 1) A Perlin noise, sampled by the density function below.
	val hills = noise("hills") {
		firstOctave = -5
		amplitudes(1.0, 0.5, 0.25)
	}

	// 2) Density functions: hills on top of a gradient turning solid into air with height.
	val terrainDensity = with(densityFunctionsBuilder) {
		val hillsNoise = noise("hills_noise", hills, xzScale = 0.35, yScale = 0.0)

		val gradient = yClampedGradient("height_gradient") {
			fromY = 0
			toY = 128
			fromValue = 1.0
			toValue = -1.0
		}

		add("final_density", hillsNoise, gradient)
	}

	// 3) Noise settings: world bounds, blocks, and the router feeding the density to the game.
	val terrain = noiseSettings("custom_terrain") {
		seaLevel = 63
		noiseOptions(minY = -64, height = 384, sizeHorizontal = 1, sizeVertical = 2)
		defaultBlock(Blocks.STONE)
		defaultFluid(Blocks.WATER) { this["level"] = "0" }

		noiseRouter {
			finalDensity(terrainDensity)
		}

		surfaceRules {
			condition(stoneDepth(Surface.FLOOR)) {
				block(Blocks.GRASS_BLOCK)
			}
			block(Blocks.STONE)
		}
	}

	// 4) A biome, used everywhere in this world.
	val plains = biome("custom_plains") {
		temperature = 0.8f
		downfall = 0.4f
		hasPrecipitation = true

		attributes {
			skyColor(0x78A7FF)
			fogColor(0xC0D8FF)
		}
	}

	// 5) The rules of the world.
	val dimType = dimensionType("custom_type") {
		minY = -64
		height = 384
		hasSkylight = true
	}

	// 6) The dimension itself.
	dimension("custom_world", type = dimType) {
		noiseGenerator(settings = terrain, biomeSource = fixed(plains))
	}
}

Go there in game with /execute in <namespace>:custom_world run tp @s 0 200 0. To offer the world as a world type in the creation screen instead, wrap the same generator in a world preset.

Testing

• /execute in <ns>:<dimension> run tp @s 0 200 0 teleports into a dimension.
• /locate structure <ns>:<structure> finds the nearest instance of a structure.
• Worldgen files are read when the world is created, so /reload does not reshape the chunks already generated. Test terrain changes on a fresh world.
• Test Features runs GameTest assertions for deterministic validation.

See Also

• Colors - the RGB and ARGB formats used by biome effects and color attributes
• Predicates - condition logic reused across the datapack
• Tags - grouping biomes, structures and presets so vanilla picks them up
• Timelines - animating environment attributes over time
• World Clocks - the clocks driving DimensionType.defaultClock