A player heads east. 500 blocks later, the server freezes for 3 seconds. TPS drops from 20 to 8. The 15 other connected players suffer the lag at the same time. The problem is not the server: it is Minecraft generating chunks on the fly, which consumes CPU for every newly discovered terrain. Chunky pregenerates these chunks in advance, before players arrive. Result: no more freezes when exploring.
Key takeaways
- Chunky pregenerates your Minecraft world's chunks before players explore them, eliminating terrain generation lag spikes.
- Three commands are enough:
chunky world,chunky radius,chunky start. - A 5,000-block radius covers the vast majority of needs for a survival server. Beyond 10,000, the storage required climbs quickly.
- Chunky works on Paper, Spigot, Fabric, Forge and NeoForge. The plugin has over 17 million downloads on Modrinth.
Why chunk generation causes lag
A Minecraft chunk is a 16×16-block column over the full height of the world (from -64 to 320 since 1.18). When a player moves in an unexplored direction, the server has to generate each new chunk in real time: terrain calculation, placement of biomes, caves, ores, structures. Each chunk takes several hundred milliseconds of CPU to generate.
On a server with a single player, it is barely noticeable. With 10 or 20 players exploring simultaneously in different directions, the processor spends its time generating terrain instead of running the game. TPS (ticks per second) drops below 20, mobs freeze, blocks are delayed in breaking, players rubber-band.
Pregenerating the world with Chunky turns this dynamic (expensive) generation into a simple disk read (almost free). Chunks are generated in advance and stored on the SSD. When a player arrives in the area, the server loads the chunk from disk instead of computing it. The performance difference is immediate.
Installing Chunky
Download Chunky from Modrinth. The plugin is also available on SpigotMC and Hangar.
- Paper / Spigot: place the .jar file in the
/plugins/folder and restart the server. - Fabric: place the .jar in the
/mods/folder. Fabric API is required. - Forge / NeoForge: place the .jar in the
/mods/folder.
Check that Chunky is loaded by typing chunky in the console. If the list of commands appears, the installation is good.
Launching a pregeneration in 3 commands
Basic setup takes 30 seconds. Three commands and the server starts working.
1. Choose the world:
chunky world world
Replace world with the name of your world (visible in the server folder). For the Nether: chunky world world_nether. For the End: chunky world world_the_end.
2. Set the radius:
chunky radius 5000
The radius is in blocks, centered on coordinates 0,0 by default. A radius of 5,000 means a square of 10,000×10,000 blocks (that is 625×625 chunks).
3. Start the generation:
chunky start
The server starts generating chunks in the background. Chunky displays progress in the console: number of chunks processed, percentage, ETA, generation speed.
Useful commands during generation
| Command | Action |
|---|---|
chunky pause |
Pauses the generation. Progress is saved. |
chunky continue |
Resumes the generation where it stopped. |
chunky cancel |
Cancels the task and erases progress. |
chunky progress |
Displays progress in game. |
chunky silent |
Hides progress messages in the console. |
chunky center 500 -300 |
Changes the center of the generation (here x=500, z=-300). |
chunky shape circle |
Generates in a circle instead of the default square. |
chunky worldborder |
Aligns the generation with the existing world border. |
chunky trim |
Deletes chunks outside the selection (cleanup). |
The chunky worldborder command is particularly handy if you have already defined a world limit with /worldborder. Chunky automatically takes the border's center and radius, which avoids configuring both separately. If you want to go further, the companion plugin ChunkyBorder replaces the vanilla world border with a customizable border (circular, polygonal shapes) that integrates directly with Chunky.
What size to pregenerate
The question everyone asks, and the answer depends on your server. Here are the orders of magnitude.
| Radius (blocks) | Area (blocks) | Chunks | Estimated storage | Estimated time |
|---|---|---|---|---|
| 1,000 | 2,000 × 2,000 | ~15,600 | ~500 MB | 5 to 15 min |
| 3,000 | 6,000 × 6,000 | ~140,000 | ~3 GB | 30 min to 1h |
| 5,000 | 10,000 × 10,000 | ~390,000 | ~8 GB | 1 to 3h |
| 10,000 | 20,000 × 20,000 | ~1,560,000 | ~30 GB | 5 to 12h |
Times vary depending on the CPU, storage (NVMe SSD vs HDD) and Minecraft version. 1.18+ generates much taller worlds (-64 to 320 instead of 0 to 256), which lengthens generation by about 30 to 40% compared with 1.17.
Our recommendation: a 5,000-block radius is the sweet spot for a standard survival server. It amply covers the first weeks of exploration without taking up excessive disk space. If you find that players reach the limit, run a second pass with a larger radius overnight.
Pregenerating with players online
Chunky can run with players online, but generation consumes CPU and can affect TPS. Two approaches.
Recommended approach: launch the pregeneration when the server is empty (at night, early morning). Chunky will use all available CPU power and finish much faster. Use chunky pause when players connect and chunky continue when they leave.
If you must generate with players online: on Paper, Chunky uses the async chunk generation API, which reduces the impact on TPS. The server stays playable during generation, but pregeneration speed will be reduced. On Spigot (which lacks Paper's async API), the impact will be more noticeable. If you are still on Spigot and pregeneration performance matters to you, that is a good reason to migrate to Paper.
Pregenerating the Nether and the End
People often forget that the Nether and the End also generate chunks on the fly. On a server where players use Nether portals to travel quickly (1 Nether block = 8 Overworld blocks), terrain generation in the Nether can cause as much lag as in the Overworld.
To pregenerate the Nether:
chunky world world_netherchunky radius 2000chunky start
A 2,000-block radius in the Nether covers the equivalent of 16,000 blocks in the Overworld. It is generally enough.
For the End, a more modest radius is enough (1,000 blocks around the End spawn). Players spend less time there and explore less far.
Frequently Asked Questions
Does pregeneration affect structures (villages, temples, strongholds)?
No. Chunky generates chunks exactly as Minecraft would when a player arrives. Structures, biomes, caves, ores and everything else are identical to what the game would produce in real time. Pregenerating does not change the world's content, it simply computes it in advance.
What happens if I update Minecraft after pregenerating?
Chunks that are already generated will not be regenerated. If the update adds new biomes or structures, they will only appear in chunks not yet generated (beyond your pregeneration radius). This is normal Minecraft behavior, not an effect of Chunky. If you want the new content everywhere, you will have to create a new world or delete the region files of the areas you want to regenerate.
Can I pregenerate several worlds at the same time?
Yes. Chunky supports parallel tasks. You can launch a pregeneration of the Overworld and the Nether simultaneously. The CPU will be more heavily used, but it is useful when the server is empty and you want to finish quickly.
Does Chunky work with world generation mods (Terralith, Biomes O' Plenty)?
Yes. Chunky does not modify terrain generation, it just asks Minecraft (or the installed generation mod) to produce the chunks. If Terralith or Biomes O' Plenty is installed, Chunky will pregenerate chunks with the mod's biomes. Make sure the generation mod is installed and configured before launching the pregeneration.
How much disk space does pregeneration take?
As a general rule, count about 1.5 to 2 MB per chunk in 1.18+. A 5,000-block radius (about 390,000 chunks) takes between 6 and 10 GB depending on the biomes and structures generated. The Nether is lighter (less world height). Use SSD storage for optimal loading times once the chunks are generated.
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