How to install a CurseForge modpack on your server

A modpack is a ready-made collection of mods, configs and often custom worlds that someone has already tested together. Installing one on a Cobbly server takes a single click — you never upload a mod file yourself — and it works on the free tier. This guide covers choosing a pack that will run well, installing it, getting your friends onto the exact same version, and the problems people most often hit on the first boot.

Before you start: will the pack fit?

Every free server has 3 GB of RAM. That decides which packs will run far more than anything else, so it is worth checking before you install:

• Light packs — performance packs, "vanilla-plus" packs, anything under about 80 mods. These run comfortably.
• Mid-size packs — roughly 80 to 150 mods. Many run, but it is tight; keep an eye on it and avoid pre-loading huge areas.
• Kitchen-sink packs — 200, 300, 400+ mods. These need 6–10 GB and will not fit in 3 GB, however they are tuned.

When you pick a large pack, the Software tab warns you that it is close to what fits in memory. The pack’s CurseForge page often lists a recommended amount of server memory too — if it says 6 GB or more, it will not run on the free tier. How much RAM does a Minecraft server need? explains where the memory goes.

Install the pack

1. Stop the server if it is running. Software changes only happen while it is stopped.
2. Open the Software tab and switch to Modpacks.
3. Search CurseForge for the pack by name, and select it.
4. Pick a version of the pack. Unless you have a reason not to, take the newest one — and note which one you chose, because your friends will need the same.
5. Press Install Modpack, then confirm.
6. Press Start.

You do not download or upload anything. Cobbly hands the pack to the server, and the server downloads and installs it on its first boot. Only CurseForge packs are available in the panel.

The first boot is slow — that is expected

The first start of a new pack downloads every mod in it and sets them all up, which can take several minutes for a larger pack. Watch progress in the Console tab. The server is ready when the console prints a line starting with Done ( — until then, players who try to join are told it is starting up.

Later starts are faster, but a modded server always takes longer to boot than Vanilla, because every mod loads each time. Pressing Start a few minutes before you play saves everyone the wait.

Server packs vs client packs

Many pack authors publish a separate server pack: the same pack with client-only mods — shaders, minimaps, menu tweaks, sound mods — already removed. When a pack version has one, Cobbly uses it, and it is marked with a Server Pack badge in the version list. That is the most reliable way to run a pack.

When a version has no server pack, Cobbly installs the regular pack and removes mods that are known to be client-only. If a client-only mod still slips through and stops the server starting, Cobbly spots the error, removes that mod and tries again automatically — a few times — before giving up. You will see this in the console as the server restarting on its own during the first boot.

Get your friends on the same pack

Everyone who joins needs exactly the same pack at exactly the same version. A different version, or one extra or missing mod, gets them rejected at the door with a "mod rejections" or "mismatched mods" message.

1. Everyone installs the CurseForge app and signs in.
2. Search for the same pack, open it, and choose the same version you installed on the server (the version drop-down on the pack’s page).
3. Play the pack once from the app, then Multiplayer → Add Server and paste your yourname.cobbly.net address.

Adding your own extra mods to the client — a minimap, say — is usually fine if they are client-only. Adding content mods (new blocks, items or mobs) on one side and not the other is what breaks joining.

Changing or updating the pack later

To move to a newer version of the same pack, stop the server and pick the new version on the Software tab the same way. Your world is kept, but read the pack’s changelog first: an update that removes a mod removes that mod’s blocks from your world too. Take a backup before any pack update, so you can go back if it goes wrong.

Switching to a different pack on an existing world rarely works — the new pack will not recognise the old one’s blocks. Start a fresh world instead, from the World tab.

If the server will not start

The status shows Crashed or Ran out of memory instead of the server reaching Done. The usual causes, in order:

• Not enough memory — the pack needs more than 3 GB. Nothing short of more memory fixes this; try a lighter pack.
• A client-only mod that the automatic clean-up did not catch. The console names it in a line mentioning invalid dist DEDICATED_SERVER. Delete that mod’s jar from the mods folder in the Files tab.
• A mod needing something missing — rare in a finished pack, more common after you add mods of your own.

Reading the console is covered step by step in Why won’t my Minecraft server start?.