Run a modpack server

A modpack is a pile of mods that were chosen to work together. Setting up a server for one by hand means matching the loader, the Minecraft version and every mod. SpawnLoft does that from a Modrinth pack in one step.

Create it

1. Choose Add a server, then From a modpack.
2. Search Modrinth for the pack. The search shows server-ready Fabric and NeoForge packs.
3. Pick one, give the server a name and some memory, and create it.

SpawnLoft builds the whole server from the pack: the loader, the Minecraft version and the mods. Press Start and watch the console.

From a terminal it is one flag:

spawnloft new packworld --modpack <slug>

Give it enough memory

Modpacks are hungrier than a plain server. The default of 4 GB is a starting point, and many larger packs want more. Look at what the pack's page recommends, set it when you create the server, and watch Stats once people are on. You can change it later under Settings, or with spawnloft set packworld memory=6G.

What your players need

Mods change the game on both sides, so your friends usually need the same pack, at the same version, installed in their own launcher. The pack's Modrinth page has the exact list and the launcher instructions. A mismatch is the most common reason a friend cannot join a modded server, and the error names a mod.

This is the main difference from a plugin server, where everyone joins with plain Minecraft. If you would rather not ask friends to install anything, choose plugins instead.

Keep the pack updated

spawnloft pack packworld
spawnloft pack packworld update --yes

The first shows the pack and checks whether a newer version exists. The second updates the server to it. Take a backup first, and read the pack's changelog: updating a pack can add and remove mods, and worlds do not always cope with mods disappearing.

spawnloft backup packworld --label before-pack-update

Adding mods on top

Modded servers get a Mods tool in place of Plugins. It searches Modrinth for mods for your loader and installs them with a snapshot beforehand, the same way plugins work. Adding to a pack is a good way to break it, so try it on a copy first.

If it will not start

Read the console with the filter on Errors, and check the troubleshooting guide. The usual causes are too little memory, the wrong Java for the Minecraft version (SpawnLoft picks the right one when it creates the server), and a mod that does not match the loader. Backups from before an update are the way back.