How to Pregenerate a Minecraft World with Chunky

To pregenerate a Minecraft world with Chunky, put the Chunky .jar in plugins (Paper, Purpur) or mods (Fabric, Forge, NeoForge), restart, then run in the console: chunky world world, chunky center 0 0, chunky radius 5000, chunky start. Then lock players inside with worldborder set 10000. The catch: Chunky's radius is half the width, while /worldborder set takes the full width, so the border number is double the radius.

What pregeneration does

When a player walks into land nobody has visited, the server has to generate those chunks on the spot: terrain, caves, structures, lighting. That work is the most common cause of lag and "Can't keep up" warnings on small servers, especially with several players exploring in different directions or flying with elytra. Pregenerating does that work once, ahead of time, so exploring only has to load chunks from disk.

That last row matters: chunks generate once. If a future Minecraft update adds new biomes or structures, they only show up in chunks generated after the update, so do not pregenerate a far bigger area than your group will use.

Before you start

• Back up. Pregeneration writes a lot of new region files. A backup makes it easy to undo.
• Pick the size. A radius of 3000 to 5000 blocks suits most friend servers. Every doubling of the radius is four times the chunks, the time and the disk.
• Pick a quiet time. Chunky uses as much CPU as it can. Run it when few people are online, or pause it when they join.
• Get the right build. Chunky is on Modrinth and Hangar for Paper, Purpur, Spigot and Folia, and as a mod for Fabric, Forge and NeoForge. Fabric needs Fabric API too. Vanilla servers cannot load it.

Step 1: Install Chunky

Stop the server, upload the jar to plugins/ or mods/, and start it. The console lists Chunky as loaded. You can run every command below in the console without the slash, or in game with a slash if you are an operator.

Step 2: Select the world and area

The full command list is on the Chunky wiki.

Step 3: Start, watch, pause

chunky start
chunky progress
chunky pause
chunky continue
chunky cancel

chunky start begins the task and prints progress, chunks per second and an estimated time left. chunky pause keeps the progress so chunky continue picks it up later, even after a restart. chunky cancel stops the task for good, but chunks already generated stay. If the console fills with progress lines, chunky quiet 60 reports once a minute, and chunky silent turns updates off.

Step 4: Set a matching world border (the gotcha)

Without a border, players walk past the edge of your pregenerated area and the server is back to generating chunks live. The vanilla world border fixes that, but its size works differently from Chunky:

/worldborder set takes the full width (diameter), and Chunky's radius is half of it. Typing the same number in both is the classic mistake: either the border is half the area you generated, or, if you set the border first and copy its number into Chunky, you generate four times the area you need. Also center the border on the same point with worldborder center 0 0.

Easier still: set the border first, then run chunky worldborder, which copies the vanilla border's center and size into Chunky's selection for you.

Step 5: The Nether and the End

Each dimension is a separate task. The Nether is scaled 1 to 8, so an overworld radius of 5000 matches a Nether radius of about 625:

chunky world world_nether
chunky radius 700
chunky start

The End's islands are mostly empty space, so many servers skip it or keep the radius small.

Common problems

• Still lagging while exploring: players are outside the pregenerated area. Check the border matches the radius, doubled.
• Chunky says the world does not exist: wrong world name for your server type. Use world_nether on Paper and minecraft:the_nether on Fabric and Forge.
• Server lags during the run: that is Chunky using spare CPU. Pause when players are on, or run it overnight.
• Disk filling up: the radius is too big for your plan. Cancel, and use chunky trim to remove chunks outside a smaller selection, then restart.
• Lag continues after pregeneration: the cause is something else, like entities or redstone. See the Minecraft server lag fix.

Pregenerating on GamezServers

On a Minecraft server from GamezServers, upload Chunky in the Files tab or over SFTP, run the commands from the panel's live console and keep an eye on RAM and CPU while it works. Click Backup first, and if a bigger radius needs more headroom, upgrade the plan and your world comes with you. For lighter mods that pair well with Chunky, see the best Minecraft server performance mods.

FAQ

Does pregenerating a world reduce lag?

Yes, for lag caused by generating new chunks while players explore. It does not fix lag from too many entities, farms or redstone.

How big should I pregenerate my Minecraft world?

A radius of 3000 to 5000 blocks suits most friend servers. Bigger areas take much longer and use much more disk.

Can I play while Chunky is running?

Yes, but the server will be slower. Use chunky pause when people play and chunky continue later.

Why does my world border not match my Chunky area?

/worldborder set uses the full width and Chunky uses the radius. Set the border to double the Chunky radius.