Adding custom world types

If your mod completely overhauls Minecraft’s worldgen, you’ll likely want to create a custom worldtype to offer users the option to use your worldgen or vanilla Minecraft’s world generation. Now, what is a custom world type you may ask? World types, also called world presets, define world generation options for Minecraft worlds. They let you change the make-up of your Minecraft worlds by configuring how world generation behaves.

Some examples of world types already built into Minecraft are “Amplified”, “Super Flat”, “Single Biome”, and “Large Biomes”.

Specifying which dimensions your world type applies to

The following block shows how to specify which dimensions your world type will apply to. In dimensions, a minecraft:overworld object is required. The dimension type can be a built-in preset or a custom dimension preset you implement in your mod.

src/main/resources/data/minecraft/example_mod/worldgen/world_preset:

{
	"dimensions": {
		"minecraft:overworld": {
			"type": "example_mod:example_mod_dimension_type"
		}
	}
}

Configuring how the worldgen works in your worldtype

generator is where you specify how the worldgen in your world type behaves. The type is a “generator ID” and the following are valid generator IDs:

  • noise
  • flat: Creates a superflat world (not really applicable here)
  • debug: Creates a debug world (not really applicable here)

In biome_source, you specify how biomes generate. The type parameter here is what kind of biome generation will be used. Valid generation types:

  • multi_noise: Similar to overworld generation
  • fixed: Like selecting “Single Biome” in world creation
  • the_end: This is the generation the end dimension uses (not really applicable here)
  • checkerboard: Places biomes in a checkerboard style

If the biome source type is minecraft:multi_noise, Minecraft will use 3D biomes in the overworld and the nether. The preset can be minecraft:overworld or minecraft:nether. More info about this can be found in the article about custom dimensions in the Minecraft wiki.

src/main/resources/data/minecraft/example_mod/worldgen/world_preset/example_mod_preset.json:

{
	"dimensions": {
		"minecraft:overworld": {
			"type": "minecraft:overworld",
			"generator": {
				"type": "minecraft:noise",
				"biome_source": {
					"type": "minecraft:multi_noise",
					"preset": "minecraft:overworld"
				}
			}
		}
	}
}

This will generate a world relatively similar to that of ‘s default overworld generation.

On a dedicated server, you navigate to your server.properties file and find the level-type field. By default, the value is minecraft:normal. Changing this to the ID for your world type (example_mod:example_mod_preset) will use that instead.

Making your worldtype accessible

In order for your world type to show in the “create a new world” screen, you will need to make a file called normal.json in resources/data/minecraft/tags/worldgen/world_preset and populate it with the following.

src/main/resources/data/minecraft/tags/worldgen/world_preset/normal.json:

{
	"values": ["example_mod:example_mod_preset"]
}

This will make your world type show up in the world creation screen.

Alternatively, if you want your world type to only show as an option while the user is holding down ALT, make a file called extended.json in the same directory as your normal.json file.