Retrogen

Bring new modded ores and structures into your existing Minecraft world.

Retrogen is a server-side mod for Minecraft 1.21.1 that adds compatible world-generation content from newly installed mods to chunks that have already been generated.

Instead of travelling far beyond your explored world, you can continue playing on the same map while Retrogen gradually adds new ores and structures as older chunks are loaded.

Main Features

Generates modded ores in existing chunks
Generates modded structures in existing chunks
Uses the original settings from each source mod
Preserves biome and height restrictions
Processes chunks gradually to reduce server lag
Prevents repeated generation
Supports custom include and exclude lists
Can adjust structures to existing terrain
Works with Fabric and NeoForge

Compatibility

Minecraft 1.21.1
Fabric — Fabric API required
NeoForge

Each loader has its own JAR file.

On dedicated servers, players do not need Retrogen installed on their clients.

Installation

Back up your world.
Install the correct Retrogen version.
Install the mods that provide the new ores or structures.
Start the world.
Check progress with:

/retrogen status

The configuration file is created automatically:

config/retrogen.json

You can reload it without restarting the server:

/retrogen reload

Configuration

Retrogen can automatically detect standard ore features from installed mods.

You can also choose exactly which mods, ores, features, and structures should be processed.

Example:

{
  "automaticNamespaces": ["create", "alexscaves"],
  "includePlacedFeatures": [
    "anothermod:*_ore"
  ],
  "excludePlacedFeatures": [
    "example:huge_test_ore"
  ],
  "includeStructures": [
    "minecraft:trial_chambers"
  ],
  "excludeStructures": [
    "example:unsafe_castle"
  ]
}

Wildcard patterns are supported:

* matches multiple characters;
? matches one character.

Performance

Retrogen processes chunks through a queue and limits how much work it performs during each server tick.

Default settings allow two operations and up to eight milliseconds of processing per tick.

These values can be changed in the configuration file.

Existing and Custom Worlds

Retrogen works with the blocks already stored in each chunk.

Modded ores will only replace blocks accepted by the original mod’s generation rules.

For imported maps and custom terrain, Retrogen can try to move surface structures up or down so they better match the actual landscape.

This adjustment is not guaranteed to work perfectly with every structure.

Important Warning

Always make a backup before installing Retrogen.

Minecraft cannot reliably tell whether a block was naturally generated or placed by a player.

Ores normally replace only suitable blocks, but structures may overlap with player builds or edited terrain.

When Retrogen is first installed in an existing modded world, it may not be able to detect every ore that was already generated. This can cause additional ore veins to appear.

Use the include and exclude settings for better control.

Limitations

Retrogen supports standard Minecraft world-generation systems such as PlacedFeature and StructureSet.

Mods that use completely custom generation events may not be supported.

Do not delete:

data/retrogen_manifest.json

This file stores Retrogen’s generation history for the world.

Do not move an already processed world between Fabric and NeoForge without creating a backup. The two loaders store chunk data differently and some content may be processed again.

Retrogen can reposition structures, but it cannot completely regenerate or blend the terrain around them.

Commands

/retrogen status
/retrogen reload