How to pre-generate your Minecraft world with Chunky

Generating new terrain is the most expensive thing a Minecraft server does. Every chunk a player sees for the first time has to be shaped, filled with caves, decorated with trees and ores, and lit — and it happens on the server while everyone is playing. Two people flying in different directions with elytra can bring a small server to its knees.

Pre-generating means doing that work in advance, while nobody needs the server to be fast. Afterwards, exploring only loads chunks from disk, which is many times cheaper. The standard tool for it is Chunky.

Install Chunky

Chunky exists for every common server type:

• Paper or Purpur — as a plugin. Upload the jar to the plugins folder.
• Fabric, Forge or NeoForge — as a mod. Upload the jar for your loader to the mods folder. It is server-side only; players do not need it.
• Vanilla — there is no plugin or mod support, so Chunky cannot run. Switch to Paper first; your world carries over.

Restart the server so it loads. You can find the jar on Modrinth or Hangar — make sure you pick the build for your Minecraft version and loader. How to add mods to your Minecraft server covers uploading.

Decide how big

Chunky’s radius is measured in blocks from the centre. A radius of 2000 makes a square 4000 blocks across. Rough sizes for the Overworld, so you can budget storage and time:

• Radius 1000 (2000 × 2000) — about 15,600 chunks. Roughly 100–200 MB on disk.
• Radius 2000 (4000 × 4000) — about 62,500 chunks. Roughly 400–700 MB.
• Radius 3000 (6000 × 6000) — about 140,000 chunks. Roughly 1–1.5 GB.
• Radius 5000 (10,000 × 10,000) — about 390,000 chunks. Several gigabytes.

The disk size depends on terrain — oceans compress well, mountains and caves less so. For a group of friends, a radius of 2000 to 3000 is usually more than they will explore in months. Each doubling of the radius is four times the chunks, the disk space and the time.

On a Cobbly free server you have 10 GB of storage for everything, including backups of the world, so stay at 3000 or below.

Run it

Type these into the server console (without the slash) or in game as an operator (with one):

1. chunky world world — choose the world. Use world_nether or world_the_end for the other dimensions on Paper.
2. chunky center 0 0 — or chunky spawn to centre on world spawn.
3. chunky radius 2000 — the radius in blocks.
4. chunky start — begin. Progress is printed to the console every few seconds, with an estimated time remaining.

While it runs: chunky pause stops it and remembers where it got to, chunky continue picks it up again, and chunky cancel abandons the task. chunky shape circle before starting generates a circle instead of a square, which saves about a fifth of the work.

How long it takes

Speed depends almost entirely on the CPU. A small server with two cores typically manages a few dozen chunks a second on Vanilla-style terrain, so radius 2000 takes somewhere around half an hour to an hour, and radius 3000 a couple of hours. World-generation mods and big modpacks can be several times slower.

The server is fully playable while Chunky runs, just slower — it is doing exactly the work you are trying to get out of the way. Running it overnight, or before inviting people, is the usual approach.

Sleeping servers stop pre-generation

On a host that puts idle servers to sleep — including Cobbly — the server only stays up while a player is online. Chunky running in the console does not count. If you start a long generation and leave, the server will save and sleep five minutes later, halfway through.

Two ways round it:

• Stay connected (AFK somewhere safe) until it finishes.
• Open plugins/Chunky/config.yml (or config/chunky.json on mods) and set continue-on-restart to true. Then Chunky resumes on its own every time the server wakes, and finishes over a few sessions.

See How sleeping servers work for when a server sleeps and wakes.

Add a world border

Pre-generating a 4000-block square does not stop anyone walking out of it. A world border at the same size does:

• worldborder center 0 0 — the same centre you gave Chunky.
• worldborder set 4000 — note the border takes the full width, so it is twice Chunky’s radius.

You can grow the border later — run Chunky again with a bigger radius first, then raise the border. Chunky skips chunks that already exist, so the second run only does the new ring.

Do not forget the Nether

The Nether is eight times smaller for travel purposes — one block there is eight in the Overworld — so a Nether radius of a quarter to an eighth of your Overworld radius covers it. The End only needs the outer islands generated if players go there often; most servers leave it alone.

Is it worth it on a small server?

If your group mostly builds around one base, the gain is small — the world around it was generated weeks ago. Pre-generation pays off on a new world, on servers where people explore a lot, and on any server where lag spikes line up with someone flying into new terrain. Why is my Minecraft server lagging? helps you tell which kind of lag you have.