Ultra Fast Pregen

Ultra Fast Pregen

Ultra Fast Pregen pre-generates your world much faster than other pre-generators by using every CPU core, so players never wait on chunk generation. The blocks, biomes and light are the same as Minecraft's own generation.

Running CraftBukkit, Spigot, Paper or Folia? Get the plugin: Ultra Fast Pregen (Bukkit)

Speed

Against Chunky (version 14, AMD Ryzen 5 7500F, NeoForge 26.1.2, a fresh 3000×3000 block area, average of 2 runs):

World	Chunky	Ultra Fast Pregen
Overworld	107.2 chunks/s	332.8 chunks/s (3.1× faster)
Overworld with Tectonic + WWOO	23.0 chunks/s	121.1 chunks/s (5.3× faster)
Nether	106.0 chunks/s	445.1 chunks/s (4.2× faster)
End	752.1 chunks/s	1,079.7 chunks/s (1.4× faster)

With C2ME installed for both: 1.1× to 1.6× faster.

Version 15 is faster than these numbers from 14: whole Overworld runs without other mods are 21% faster on NeoForge 26.1.2 and 17% faster on Fabric 26.2 (i9-11900T, 16 threads, 2,000 × 2,000 blocks). In All the Mods 9: 51.5 → 60.1 chunks/s (+17%).

On different CPUs (3000×3000 blocks, earlier versions):

CPU	Area (block)	Time	Speed
AMD Ryzen 5 7500F (6 cores / 12 threads)	3000×3000	1 min 54 s	308.8 chunks/s
AMD Ryzen 5 7530U (6 cores / 12 threads)	3000×3000	3 min 01 s	195.2 chunks/s
Intel Core i9-11900T ES (8 cores / 16 threads)	3000×3000	5 min 02 s	116.9 chunks/s
Intel Xeon (hosted, 4 vCPU 3.00Ghz)	3000×3000	9 min 17 s	63.3 chunks/s

It uses all cores, so it is best run before players join, or while few are online. It runs on the CPU only (no GPU).

Features

• Vanilla-matching worlds. Terrain, biomes, structures, caves, features and light are checked block for block against vanilla, including large biomes, amplified, nether, end, caves and floating islands.
• Any radius, square or circle. Set the radius in blocks, take the area from the world border, or center it on the world spawn. Trees along a circle's edge are not cut off.
• Resumable. Stop at any time and continue with /pregen resume. A run cut short by a server stop or crash continues by itself once the server is back.
• Safe with existing worlds. Chunks that already exist are kept, and new terrain joins them without a visible seam.
• Seamless borders. Trees, ores and other large features are not cut off where generation areas meet.
• Low-memory friendly. Automatically adjusts to the memory available, down to a 2 GB heap.
• Works with other mods. Detects mods that change world generation and adapts, including Lithium, SuperChunk and big modpacks. If a batch still fails because of another mod, it is generated again the way Minecraft does instead of stopping.
• C2ME, Distant Horizons and Voxy. C2ME is supported, chunk storage included; on the 26.x builds, generated chunks go straight into Distant Horizons' LoD (and Voxy's, in singleplayer).
• API for other mods. Start and stop runs, follow their progress, receive every saved chunk (for map and LoD mods), and declare how their own world generation changes work with the fast paths.
• Any dimension. Overworld, Nether, End and modded dimensions.

Tested with

All six builds, in the Overworld, Nether and End, with every saved chunk checked: C2ME, Lithium / Canary, Noisium, FerriteCore, ModernFix, Starlight / ScalableLux, Distant Horizons, Voxy, Terralith, Biomes O' Plenty, YUNG's Better Caves and Alex's Caves (132 of 132 runs passed with version 15), and the All the Mods 9, All the Mods 10 and Prominence II modpacks. Full results: https://github.com/Pongsapat3791/Ultra-Fast-Pregen/blob/main/COMPATIBILITY.md

Not supported yet: Moonrise (it replaces Minecraft's chunk system); /pregen start says so and starts nothing. Paper and Folia, which have it built in, are supported by the Bukkit plugin.

Commands (op level 2; in singleplayer the world's owner, cheats or not)

Command	What it does
/pregen radius <blocks>	The radius of the next /pregen start
/pregen shape <square|circle>	A square, or a circle (every chunk whose center lies within the radius)
/pregen worldborder	Take the center and size from the world border
/pregen spawn	Center on the world spawn
/pregen start	Generate the chosen area around the center
/pregen start <world_k>	Generate an area world_k x 1000 blocks across around the center
/pregen resume	Continue the last run
/pregen stop	Stop after the current batch
/pregen status	Progress, speed, ETA and memory
/pregen center [x z]	Set the center (default 0 0)
/pregen world [dimension]	Choose the dimension
/pregen reset	Forget which chunks were pre-generated
/pregen set [key value]	Show or change a setting of the config file

Operators see the progress, speed and ETA on a boss bar.

Example

Command	What it does
/pregen radius 2500, /pregen shape circle, /pregen start	Generate every chunk within 2,500 blocks of the center
/pregen start 4	Generate a 4000 x 4000 block square around the center
/pregen world minecraft:the_nether then /pregen start 4	Generate a 4000 x 4000 block square in the Nether

Config

config/ultrafastpregen.conf, reloaded on every start (or change it with /pregen set):

Key	Default	Meaning
batch_size	1000	Size of each generation step in blocks (512-10000)
threads	max	Worker threads
skip_existing_chunks	true	Keep existing chunks; false overwrites the whole area
parallel_steps	true	Structures, caves and features on all threads; false if a worldgen mod crashes
terrain_pipeline	auto	auto picks the fast path when it is safe; vanilla always uses Minecraft's own steps
resume_after_restart	true	Continue a run cut short by a server stop or crash once the server has started

Versions

Loader	Minecraft	Java
Fabric (no Fabric API needed)	1.20 to 1.20.6, one jar	17+ (21+ from 1.20.5)
Forge	1.20 to 1.20.4, one jar	17+
Fabric (no Fabric API needed)	1.21 and 1.21.1, one jar	21+
NeoForge	1.21 and 1.21.1, one jar	21+
NeoForge	26.1.2 and 26.2, one jar	25+
Fabric (no Fabric API needed)	26.1 to 26.2, one jar	25+

Server side only: players do not need it. It also works in singleplayer.

Also as a plugin for CraftBukkit, Spigot, Paper and Folia 26.2, one jar for all four: Ultra Fast Pregen (Bukkit)

Link and Manager

Two mods that work with Ultra Fast Pregen 15.1 or later. Install them next to it; players do not need them.

• Ultra Fast Pregen Link: generates the world outside the world players are in, on this server or on others, then adds only the chunks the world does not have yet.
• Ultra Fast Pregen Manager: a web page inside your server. Pick an area on a map, press Start, and watch the run. It also shows the machines of a Link network and which of them generates what.

Notes

• It uses all CPU cores, so the server may stutter if players are online. Lower threads by 1-2 if needed.

• Chunks currently loaded by a nearby player may not receive features from newly generated neighbors.

• Memory: 4 GB recommended for the server, for example:

  java -Xms4G -Xmx4G -jar server.jar nogui

  More memory lets it use a larger batch for slightly better speed. With less than 4 GB the batch size is lowered automatically and generation is a little slower.

Source, test results and benchmark tool: https://github.com/Pongsapat3791/Ultra-Fast-Pregen · License: LGPL-3.0