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

1. Back up your world.
2. Install the correct Retrogen version.
3. Install the mods that provide the new ores or structures.
4. Start the world.
5. 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

Retrogen

Add ores and structures from newly installed mods to your existing Minecraft world.

Retrogen is a server-side world-generation mod for Minecraft 1.21.1. It processes already generated chunks as they are loaded and adds compatible ores and structures from mods that were installed later.

Normally, new world-generation content only appears in unexplored areas. Retrogen allows you to continue using your existing world without travelling thousands of blocks just to find newly added resources or structures.

Features

• Adds modded ores to existing chunks
• Adds modded structures to existing chunks
• Uses the original generation settings from the source mod
• Preserves biome, height, frequency, spread, and block replacement rules
• Supports imported and custom terrain
• Can adjust surface structures to match the existing landscape
• Processes chunks gradually to reduce server lag
• Remembers completed generation attempts
• Prevents repeated generation of the same content
• Supports configurable include and exclude lists
• Supports Fabric and NeoForge

Supported Versions

• Minecraft 1.21.1
• Fabric with Fabric API
• NeoForge

Fabric and NeoForge use separate JAR files.

On a dedicated server, Retrogen only needs to be installed on the server. Players do not need to install it on their clients.

For single-player worlds, install Retrogen in the client’s mods folder.

How It Works

When an existing chunk is loaded, Retrogen adds it to a processing queue.

The chunk is processed only after it is fully loaded. Retrogen limits both the number of operations and the amount of processing time used during each server tick.

Ore generation uses the original PlacedFeature settings provided by the source mod. This means Retrogen keeps the intended:

• generation height;
• vein size;
• frequency;
• biome restrictions;
• block replacement rules.

Structures are created through Minecraft’s standard structure-generation system.

Retrogen stores processed content inside each chunk and keeps the world’s generation history in:

data/retrogen_manifest.json

This prevents the same ore or structure from being generated every time the chunk loads.

Installation

1. Back up your world.
2. Install the correct Retrogen JAR.
3. Install the mods that provide the new ores and structures.
4. Start the server or single-player world.
5. Check the processing queue with:

/retrogen status

For Fabric, Fabric API is also required.

Retrogen creates its configuration file automatically:

config/retrogen.json

Configuration

Default configuration:

{
  "enabled": true,
  "generateOres": true,
  "generateStructures": true,
  "adaptStructuresToExistingTerrain": true,
  "maxOperationsPerTick": 2,
  "maxMillisPerTick": 8,
  "structureReferenceRadius": 8,
  "maxTerrainShift": 96,
  "maxTerrainSampleSpread": 32,
  "maxInhabitedTimeTicks": -1,
  "automaticNamespaces": ["*"],
  "excludedNamespaces": ["minecraft", "retrogen"],
  "includePlacedFeatures": [],
  "excludePlacedFeatures": [],
  "includeStructures": [],
  "excludeStructures": []
}

Retrogen automatically selects standard modded ore features from allowed namespaces.

You can restrict automatic processing to specific mods:

{
  "automaticNamespaces": ["create", "alexscaves"]
}

You can also manually include or exclude individual features and structures:

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

The lists support wildcard patterns:

• * matches any number of characters;
• ? matches one character.

Reload the configuration without restarting the server:

/retrogen reload

Custom and Imported Terrain

Ores are generated in the blocks that already exist inside the chunk.

A modded ore can only replace blocks accepted by the source mod’s generation rules. For example, an ore configured to replace normal Minecraft stone may not generate inside custom stone blocks.

Retrogen can also adjust surface structures to match the real terrain instead of relying only on the current chunk generator.

When enabled, Retrogen samples the existing surface or ocean floor and moves the structure vertically when necessary.

This is a best-effort system. Some unusual structures may still require special support from their original mod developer.

Important Warning

Always create a backup before using Retrogen.

Minecraft cannot reliably distinguish naturally generated blocks from blocks placed by players.

Ores normally replace only valid target blocks, but structures may intersect:

• player buildings;
• roads;
• farms;
• underground bases;
• other edited terrain.

On its first installation, Retrogen may not know which modded ores were already present when older chunks were created. Existing modded worlds may therefore receive additional ore veins.

Use the include and exclude lists when working with an important world.

Limitations

Retrogen supports content registered through standard Minecraft world-generation systems such as:

• BiomeGenerationSettings;
• PlacedFeature;
• StructureSet.

It cannot automatically reproduce content generated through completely custom mod events or independent generation systems.

Changing generation settings while keeping the same registry ID does not automatically trigger another generation pass.

Do not delete:

data/retrogen_manifest.json

This file stores the world’s Retrogen history.

Retrogen does not force-load distant chunks to complete structures. Very large structures may require both their starting chunk and distant piece chunks to be loaded at the same time.

Retrogen can move structures vertically, but it cannot regenerate natural terrain blending around them.

Do not move an already processed world between Fabric and NeoForge without a backup. The two loaders store Retrogen’s chunk markers differently, which may cause content to be processed again.

Commands

/retrogen status

Shows the current processing queue.

/retrogen reload

Reloads the configuration and available content catalogue.