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This feature is exclusive to Java Edition.

Custom is a world type that allow users to change the generation of the Overworld, Nether, and End dimensions as well as the ability to create custom dimensions. It is edited using a JSON file that is imported on the world creation screen.


Custom world generation works using JSON files, which need to be imported before world creation.

In the world creation menu, go to more options and select the "Import World" option. Then, select a world generation JSON file. A warning appears saying that custom worlds are experimental. Click "Yes" to continue.

The only way to access added dimensions is through commands, such as /execute in <dimension name> run tp @s ~ ~ ~, which teleports the player to the specified dimension (see § JSON format).

JSON format[edit]

This section needs expansion with:
explanations on each component of the JSON file. Useful sources: [1], [2].
You can help by adding to it.

Custom generation files take the following format:

  • The root tag.
    •  bonus_chest (Boolean): Whether the world has a bonus chest or not (equivalent to the "Bonus chest" option).
    •  generate_features (Boolean): Whether structures should be generated or not (equivalent to the "Generate structures" option).
    •  seed (integer): The numerical seed of the world.
    •  legacy_custom_options (string): The custom world preset that was used to generate the world when it was an old customized world. Exists only for old customized worlds.
    •  dimensions: A list of the dimensions in this world where the key is the namespace ID of the dimension.
      • A dimension. The dimensions minecraft:overworld, minecraft:the_nether and minecraft:the_end are required for a well functioning world. Any other namespaced ID is allowed for custom dimensions.
        •  generator: Generation settings used for that dimension.
          •  type (string): The ID of the generator. Can be minecraft:flat for a superflat dimension, minecraft:noise for noise generation, or minecraft:debug for a debug dimension.
          • Other compounds (see below)
        •  type: This can be a list of options for the dimensions, the namespaced ID of a dimension type file in a data pack, or one of the four default dimension types (minecraft:overworld, minecraft:the_nether, minecraft:the_end, minecraft:overworld_caves).
          •  name: The resource location used for the dimension type. Required only when importing world settings.
          •  ultrawarm: Whether the dimensions behaves like the nether (water evaporates and sponges dry) or not. Also causes lava to spread faster and thinner.
          •  natural: When false, compasses spin randomly. When true, nether portals can spawn zombified piglins.
          •  coordinate_scale: The multiplier applied to coordinates when traveling to the dimension.
          •  has_skylight: Whether the dimension has skylight access or not.
          •  has_ceiling: Whether the dimension has a bedrock ceiling or not.
          •  ambient_light: How much light the dimension has, default is 0.5 in the demo file (for upper and lower bounds as well as precise effect[needs testing]).
          •  fixed_time (optional): Can be false or any integer from 0 to 24000. If this is set to a number, the time of the day is the specified value. However, in at least some worlds,[needs testing] false is interpreted as 0, giving constant sunrise. To ensure a normal time cycle, leave the attribute undefined (i.e, do not include it).
          •  piglin_safe: Whether piglins shake and transform to zombified piglins.
          •  bed_works: Whether players can use a bed to sleep.
          •  respawn_anchor_works: Whether players can charge and use respawn anchors.
          •  has_raids: Whether players with the Bad Omen effect can cause a raid.
          •  logical_height: The maximum height to which chorus fruits and nether portals can bring players within this dimension. This excludes portals that were already built above the limit as they still connect normally.[needs testing]
          •  infiniburn: A resource location defining what block tag to use for infiniburn.

Generator types[edit]

The format of the  generator compound is dependent on the value of its generator ID, or  type.

When the generator ID type is minecraft:noise:

  •  generator: Generation settings used for the dimension.
    •  type (string): The ID of the generator (in this case, minecraft:noise).
    •  seed: The seed used to generate the dimension. In most cases, this is exactly the same as the world seed, but can be different and the dimension generated is based upon this seed and not the world seed.[needs testing]
    •  settings: The noise settings used in the terrain generator. Can be set to a string to use a preset defined in the worldgen/noise_settings folder with a list of customized options. See Custom world generation#Noise settings for more information.
    •  biome_source: Settings dictating which biomes and biome shapes.
      •  seed (integer): The seed used for biome generation. In most cases, this is exactly the same as the dimension seed (and by extension the world seed), but can be different and the biome generation for this dimension is based upon this seed and not the dimension seed.[needs testing]
      •  type (string): The type of biome generation. Arguments lie in the biome_source compound. Some possible values for type include minecraft:vanilla_layered, minecraft:fixed, minecraft:checkerboard, minecraft:multi_noise, and minecraft:the_end.
        • vanilla_layered: Default and large biome generation used in the overworld.
          •  large_biomes (Boolean): Whether the biomes are large. True for biomes generation in the "Large Biomes" world type.
          •  legacy_biome_init_layer (Boolean): Whether the world was default_1_1.[needs testing]
        • multi_noise: 3D biome generation used in the nether.[needs testing]
          •  preset (string): A preset of the set of biomes to be used, mutually exclusive with  biomes[needs testing] the only valid that's currently supported is minecraft:nether.
          •  biomes: A list of biomes, including their likelihood.
            • : A biome and its properties
              •  biome (string): The biome.
              •  parameters: Represent optimal conditions for where the biome should be placed. These values do not affect the generation of terrain within biomes; they affect where the game chooses to place biomes. altitude, weirdness, humidity and temperature are each represented in a distinct contoured map generated by the seed. At any specific point, the biome having parameters most closely resembling the respective parameter on each noise map at that point is chosen. For example, if the point were to have values of -1 temperature, 0.2 humidity, 0.5 altitude and 0 weirdness then birch_forest_hills (-0.1t,0.2h,0.25a,0w) would be chosen over desert (0.5t,-0.5h,0a,0w).
                •  altitude (float): Used to place similar biomes near each other. Range: (-2.0 to 2.0). [needs testing]
                •  weirdness (float): Defines how weird the biome is going to appear next to other biomes. Range: (-2.0 to 2.0).
                •  offset (float): Range: (0.0 to 1.0). Similar to the other parameters but offset is 0 everywhere, thus setting this parameter nearer to 0 gives the biome a greater edge over others, all else being equal.
                •  temperature (float): Used to place similar biomes near each other. This is NOT the same as the temperature value listed on Biome, it does NOT affect rain/snow or the color of leaves and grass.
                •  humidity (float): Used to place similar biomes near each other.[needs testing]
          •  altitude_noise: [needs testing]
          •  weirdness_noise: [needs testing]
          •  temperature_noise: [needs testing]
          •  humidity_noise: [needs testing]
        • the_end: Biome generation used in the end with biome minecraft:the_end in the center and other end biomes around.[needs testing]
        • fixed: a single biome.
          •  biome: The single biome to generate.
        • checkerboard: A biome generation in which biomes are square (or close to square) and repeat along the diagonals.
          •  biomes: A list of biomes that repeat along the diagonals (can be more than 3).
          •  scale: Determines the size of the squares on an exponential scale.


When the generator ID type is minecraft:flat (used for Superflat world generation):

  •  generator: Generation settings used for the dimension.
    •  type (string): The ID of the generator (in this case, minecraft:flat).
    •  settings: Superflat settings.
      •  layers: Layer settings.
        • : A superflat layer. This list is interpreted from top to bottom.
          •  height: The number of blocks in the layer.
          •  block: The block the layer is made of.
      •  biome: the single biome of the world
      •  lakes (optional): Whether or not to generate lakes. If set to true, then water and lava lakes generate often even in biomes where lakes don't normally generate. Lava lakes generate surrounded by different types of stone and ores from the overworld.
      •  features (optional): Whether or not to generate biome-specific decorations like trees, grass, flowers, cacti, etc.
      •  structures: Structure settings
        •  stronghold: Settings for how strongholds should be spawned. The stronghold values under the structures tag appear to be placeholders so that every namespaced structure has a value; these values are the ones that actually control stronghold spawning.
        •  structures: List of structures to use in this dimension
          •  <namespaced id>: The key for this field should be the namespaced ID of a structure, a list is available at Java Edition data value § Structures. If structures are not listed, it does not generate.
            •  spacing (number): Average distance between two structure placement attempts of this type in chunks[note 1].
            •  separation (number): Minimum distance between two structures of this type in chunks; must be less than spacing.
            •  salt (integer):[needs testing] A number that assists in randomization; see salt (cryptography).

When the generator ID type is minecraft:debug (used for Debug world generation):

  •  generator: Generation settings used for the dimension.
    •  type (string): The ID of the generator (in this case, minecraft:debug).


Moved to Custom world generation#Noise settings

Noise generator preset defaults[edit]

These are the settings used by the 6 presets available for the minecraft:noise generator.

Structure defaults[edit]

These are the default values for all namespaced structures. Every preset uses the same values for all of these structures, with the exception of minecraft:ruined_portal.

*Placeholder values, have no effect

**Salt values aren't used for theses structures; changing them produces no effect }}

Biome parameter defaults[edit]

These are the default values used for each biome in the multi_noise biome_source. Interestingly, although only the values for nether biomes are accessible through a preset, several overworld biomes have default values as well.

Type defaults[edit]

These are the settings used by the 3 dimensions present in Vanilla.


This section needs expansion with:
more examples and the actual info for what the default generator uses..
You can help by adding to it.

Default settings[edit]

The following is the settings for an exported default Minecraft world.

Expanded default settings[edit]

This file contains the same settings used to produce a default world, but with all of the presets expanded to their default values. Note that there is a bug that makes it impossible to create the ender dragon fight without using the dimension type preset minecraft:the_end, as the flag that creates the fight is hardcoded and not accessible through JSON. However, it is otherwise identical to the default world.

Custom superflat dimension[edit]

An overview of a world made with the adjacent settings.

This dimension is a Superflat world with a layer of grass on four layers of coarse dirt on top of five layers of basalt. The entire world is full of village houses as spacing is set to 3 (default: 32) and separation is set to 1 (default: 8). The words starts by default at time 1000.


Java Edition
2018The return of customized worlds was mentioned.[1][2][3]
1.1620w21aAdded custom worlds.
Custom worlds are JSON-driven.
Custom dimensions can be added and vanilla dimensions can be modified.
There is currently no in-game menu to modify worlds; custom worlds can be generated only by importing a JSON file.
pre1The "temparature" biome parameter is now spelled "temperature".
Dimensions and dimension settings can be created through data packs.
1.16.220w28aExperimental custom biome support is now included in custom worlds.


Issues relating to "Custom" are maintained on the bug tracker. Report issues there.

External links[edit]

See also[edit]


  1. Setting this to a number does not mean one structure is generated this often, only that the game attempts to generate one; biomes or terrain could lead to the structure not being generated. The maximum distance of structure placement attempts is 2*spacing - separation.
  1. "Customized worlds will be returning. I can't speak for the extra options you mentioned though." – u/AlmightyZing
    "But after 1.13"u/_Grum on Reddit, May 15, 2018
  2. "Would you really not consider holding off 1.13 until customised worlds are finished? Seems pretty crazy to set a precedent for the chance of losing features for several updates.
    We came so close to having access to customising structures in world gen this update too, a shame that hasn't made the cut" – u/DaUltraMarine
    "No, they will come back but completely different from before."u/_Grum on Reddit, May 15, 2018
  3. "No customization until after 1.13, or the other things?" – u/Kobbett
    "No more screens with 50 vague sliders indeed."u/_Grum on Reddit, May 15, 2018