When a player walks into terrain nobody has visited before, your server has to build that terrain right there and then — while it is also running mobs, redstone and everything else. Chunk generation is the single most CPU-hungry thing a Minecraft server does, and it is why exploring feels laggy even on a machine that idles at 20 TPS.
Chunky fixes this permanently. It generates the world ahead of time, in the background, so that by the time players get there the terrain already exists on disk. This guide covers every command, the radius worth choosing, and the mistakes that make people think Chunky is broken when it isn't.
What Chunky actually does
Chunky is a free plugin (Bukkit, Spigot, Paper, Purpur) that also exists as a Fabric, Forge and NeoForge mod. It walks your world outward from a center point and forces the server to generate every chunk inside the radius you set. Once a chunk exists, visiting it costs almost nothing — the server just reads it from disk instead of calculating a new piece of world.
It does not change your terrain, your seed or your generation settings. It only does early what the server would otherwise do later, at the worst possible moment.
Installing it
- Paper / Spigot / Purpur: drop the Chunky
.jarinto/pluginsand restart. That is the whole install. - Fabric / Forge / NeoForge: drop it into
/mods. On Fabric it needs Fabric API. - Chunky runs from the server console too, so you do not need to be in game or have operator rights.
The commands you will actually use
/chunky radius 3000— sets how far out to generate, in blocks, from the center./chunky start— begins generating./chunky progress— shows percentage done, chunks per second and an ETA./chunky pause— stops for now and remembers where it was./chunky continue— resumes from where it paused./chunky cancel— stops and discards progress for that world./chunky world the_nether— switches which world the next commands apply to./chunky center 0 0— sets the center point. Defaults to world spawn./chunky shape square— square or circle. Square pairs naturally with a square world border./chunky quiet 30— how often, in seconds, it prints progress to console.
A complete run is usually three lines: set the radius, start, and check progress once in a while.
Choosing a radius
Bigger is not better. Every chunk you pregenerate is disk space you pay for and time the CPU spends. The radius that fits your server depends on how many people play and how much they roam:
- Small SMP, 2-10 friends: 2000-3000 blocks. Plenty for months of play.
- Public survival, 10-40 players: 5000 blocks, paired with a world border.
- Large community or an exploration-heavy modpack: 8000-10000 blocks, and expect several hours plus real disk usage.
As a rough sense of scale, a 5000-block radius is around 98 million blocks of surface area and tends to land in the low tens of gigabytes on a modded world. Check your plan's disk before starting a huge run.
Do the Nether and the End separately
This is the step most people miss. Chunky works on one world at a time, and the Nether is where the worst generation lag usually happens because every block travelled equals eight in the Overworld. Run it explicitly:
/chunky world the_netherthen/chunky radius 1000and/chunky start/chunky world the_endthen a smaller radius, if your players use the End at all
A Nether radius of about one eighth of your Overworld radius covers the same travel distance.
Pair it with a world border
Pregenerating is pointless if players can simply walk past the edge of what you generated — they will hit ungenerated terrain and the lag comes right back. Set a border that matches:
/worldborder set 6000 for a 3000-block radius. The border command takes a diameter, so it is always your Chunky radius times two. Do it for every world you pregenerated.
Run it on an empty server
While Chunky is working it will use as much CPU as you let it, and TPS will drop for anyone online. Start it when nobody is playing — overnight is ideal — or throttle it so it runs politely alongside players:
- Lower the generation rate in Chunky's
config.ymlif you must run it during peak hours. - Announce a maintenance window. A pregeneration that takes two hours at full speed can take all day when throttled.
- Progress survives restarts, so a long run does not have to happen in one sitting — pause it, restart, continue.
How long it takes
There is no single answer, because it depends almost entirely on single-core CPU speed and on how heavy your world generation is. Vanilla terrain is fast; a modded world with custom biomes, ore distribution and structure mods can be five to ten times slower for the same radius. Expect minutes for a small vanilla radius and several hours for a large modded one. Watch /chunky progress for the first few minutes: the chunks-per-second figure it reports lets you extrapolate the rest accurately.
Common problems
- "Unknown command" — the plugin did not load. Check the console at startup for a Chunky line and confirm you used the build that matches your server type (plugin vs mod).
- It seems stuck at the same percentage — on modded worlds this is normal in dense structure areas. Confirm with
/chunky progressthat chunks per second is above zero before assuming a freeze. - The server ran out of disk — cancel, trim the radius and start again. Pregenerated chunks stay on disk permanently.
- Lag is still there afterwards — then generation was not your bottleneck. Entities, unoptimised plugins and view distance are the usual suspects.
What to do after pregenerating
Pregeneration removes one specific cause of lag. If your TPS still dips, the next things worth checking are your view-distance (6-8 is plenty), your simulation-distance (5-6), whether you are on Paper rather than vanilla Spigot, and whether some farm is spawning thousands of entities. A Spark profile will tell you in one minute what guesswork takes a week to find.
A note on hardware
Chunk generation is almost purely single-core CPU work, which is why two servers with the same RAM can pregenerate at completely different speeds. At TaroHosting every server sits on a Ryzen node picked for per-core performance, and support will happily run a pregeneration for you if you would rather not babysit it — just ask on Discord.