Minecraft World Generation

Use this skill for biome, dimension, feature, or structure data and their registration. Use minecraft-datapack for non-worldgen data and minecraft-modding for non-worldgen gameplay code.

Routing Boundaries

• Use when: the task changes worldgen data, registration, or injection.
• Do not use when: the task is non-worldgen datapack work (minecraft-datapack).
• Do not use when: the task is non-worldgen mod systems (minecraft-modding).

Choose the delivery path

Worldgen registries are datapack registries: their files load at world load and their registry path determines the data path. Read the NeoForge registry guide before choosing a mod-specific registry path.

Version boundary

Use Minecraft 26.x for new work. Use Java 25 and start each JSON schema from the exact target's vanilla data or generated output. Do not copy a 1.21 shape into a 26.x pack merely because it parses as JSON.

Preserve an established 1.21.x project on Java 21 and its matching schema unless the task explicitly includes an upgrade. Keep examples matched to the project version.

The 26.1 migration primer removes minecraft:random_patch and minecraft:no_bonemeal_flower. It replaces the random-patch pattern with a separate minecraft:simple_block configured feature and placements for count, random offset, and block-predicate filtering. Inspect the relevant primer section before migrating code or data.

Read legacy 1.21 JSON patterns only when the project targets that version. Those examples are not release artifacts for 26.x.

Data layout and reference graph

26.3 uses worldgen/feature/; through 26.2 this was worldgen/configured_feature/. In 26.3, feature fields are at the root, block states use id / properties, and biome spawn settings belong in environment attributes. See the 26.3 migration primer.

data/<namespace>/
├── worldgen/
│   ├── biome/
│   │   └── my_biome.json
│   ├── feature/
│   │   └── my_ore.json
│   ├── placed_feature/
│   │   └── my_ore_placed.json
│   ├── noise_settings/
│   │   └── my_dimension_noise.json
│   ├── structure/
│   │   └── my_structure.json
│   ├── structure_set/
│   │   └── my_structures.json
│   ├── processor_list/
│   │   └── my_processors.json
│   ├── template_pool/
│   │   └── my_pool.json
│   └── carver/
│       └── my_carver.json
├── dimension/
│   └── my_dimension.json
├── dimension_type/
│   └── my_type.json
├── tags/
│   └── worldgen/
│       └── biome/
│           └── is_forest.json
└── neoforge/
    └── biome_modifier/      (NeoForge mod only)
        └── add_ores.json

Build and review the graph from its leaves upward:

1. Define a feature, then its placed feature.
2. Reference placed features from a biome or biome modifier at the intended decoration step.
3. Define a structure, then its structure set; a jigsaw structure also needs a template pool, processor list, and structure template.
4. Define a dimension type and noise settings before a dimension that references them.

Use fully qualified identifiers across namespaces. An external minecraft: or dependency reference is valid when that dependency supplies the registry entry; do not create a local copy merely to satisfy static checking. If the same pack contains that external namespace and registry directory, treat it as local and verify the target exists.

Biomes and dimensions

For 26.x biome and dimension data, use the exact target's vanilla data or datagen output as the schema source. The older effects and dimension-type fields do not model newer environment behavior. The 11 decoration steps still organize placed features; choose the semantically appropriate step and keep ore placement in underground_ores.

The version-labeled 1.21.5 biome and dimension examples are in legacy 1.21 JSON patterns.

26.3 feature pattern

This berry-bush example follows the 26.3 vanilla data. Keep older packs on their original schema; do not port them by changing metadata alone.

At data/<namespace>/worldgen/feature/my_plant.json:

{
  "type": "minecraft:simple_block",
  "to_place": {
    "id": "minecraft:sweet_berry_bush",
    "properties": { "age": "3" }
  }
}

At data/<namespace>/worldgen/placed_feature/my_plant.json:

{
  "feature": "<namespace>:my_plant",
  "placement": [
    { "type": "minecraft:count", "count": 96 },
    {
      "type": "minecraft:offset",
      "x": { "type": "minecraft:trapezoid", "min": -7, "max": 7, "plateau": 0 },
      "y": { "type": "minecraft:trapezoid", "min": -3, "max": 3, "plateau": 0 },
      "z": { "type": "minecraft:trapezoid", "min": -7, "max": 7, "plateau": 0 }
    },
    {
      "type": "minecraft:block_predicate_filter",
      "predicate": {
        "type": "minecraft:all_of",
        "predicates": [
          { "type": "minecraft:matching_block_tag", "tag": "minecraft:air" },
          { "type": "minecraft:matching_blocks", "blocks": "minecraft:grass_block", "offset": [0, -1, 0] }
        ]
      }
    }
  ]
}

NeoForge biome modifiers

Biome modifiers load from data/<modid>/neoforge/biome_modifier/<path>.json. They can target a biome id or tag and add or remove placed features, among other changes. The current Biome Modifiers guide documents their schemas, decoration steps, and datagen.

For neoforge:add_features, features accepts a placed-feature id, list, or tag. Vanilla placed features may be referenced in biome JSON or added with a modifier, but NeoForge cautions against doing both because feature-order cycles can crash world loading. Prefer a copy under the mod namespace when an injected vanilla feature would create that risk.

When targeting a biome from an optional dependency, put the target in a biome tag entry with required: false, then use that tag in the modifier. This lets the pack load when the dependency is absent.

Structures and dimensions

For any current release, derive structure, template-pool, dimension, and dimension-type JSON from that release's vanilla data or datagen output. Confirm the reference graph before launching a test world:

• structure_set references structure.
• Jigsaw start_pool references template_pool; each single-pool element references its structure template and processor list.
• dimension.type references dimension_type; a noise generator's string settings references worldgen/noise_settings.

For Fabric registration or mod datagen, use the exact loader and API version's documentation rather than copying 1.21 code into a 26.x project.

The detailed 1.21 structure and dimension examples are in legacy 1.21 JSON patterns.

Development Workflow

1. Create or edit worldgen JSON files in data/<namespace>/worldgen/ (or equivalent mod resources path).
2. Run the bundled validator to catch JSON and cross-reference errors before loading:

   ./scripts/validate-worldgen-json.sh --root /path/to/datapack-or-mod-resources --feature-registry feature
   # Strict mode treats warnings as failures:
   ./scripts/validate-worldgen-json.sh --root /path/to/datapack-or-mod-resources --feature-registry feature --strict
   

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   Omit --feature-registry feature for packs through 26.2.
3. Fix any reported errors and re-validate until clean. The validator checks:
   • JSON validity for worldgen/** and neoforge/biome_modifier/**
   • Cross-reference integrity for placed_feature -> feature (or legacy configured_feature)
   • Cross-reference integrity for structure_set -> structure and biome/biome_modifier feature targets
   • Cross-reference integrity for jigsaw structure -> start_pool and template_pool -> structure template / processor_list
4. Compare biome and dimension-type JSON against the exact target's vanilla registry shape before in-game testing. The helper does not run Mojang codecs: valid JSON and local references do not prove that fields such as carvers, effects, or dimension settings match that release's schema.
5. In-game biome and structure testing:

   /locate structure <namespace>:my_structure
   /locate biome <namespace>:my_biome
   /place feature <namespace>:my_ore
   

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   place feature takes a feature ID (configured_feature through 26.2), not its placed-feature wrapper.
6. For dimension testing, use /execute in (dimension must exist at world load, not added via /reload):

   execute in <namespace>:my_dimension run tp @s 0 100 0
   

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7. Check latest.log for worldgen errors (missing biome references, malformed noise settings).
8. Note: /reload refreshes datapack JSON but does not re-generate already-generated chunks. Test new worldgen in a fresh world or newly generated chunks. For existing test worlds, use a disposable copy and a purpose-built chunk reset/regeneration workflow; /fill only replaces blocks and is not a substitute for world generation.

References

• Minecraft Wiki — World generation: https://minecraft.wiki/w/Custom_world_generation
• Minecraft Wiki — Biome: https://minecraft.wiki/w/Biome/JSON_format
• Minecraft Wiki — Features: https://minecraft.wiki/w/World_generation/Configured_feature
• NeoForge Biome Modifiers: https://docs.neoforged.net/docs/worldgen/biomemodifier/
• Fabric BiomeModifications: https://wiki.fabricmc.net/tutorial:biomemodification
• misode's data pack generator (worldgen UI): https://misode.github.io/worldgen/