How to install Forge mods on a Minecraft server

To add mods to a Forge server, upload each mod's .jar into the mods folder with the file manager and restart. Players need the same mods, at the same versions, installed on their own Forge client.

Before you start

Create your server from the Forge template. Plugins for Paper do not work on Forge, and Forge mods do not work on Paper.
Start the server once so it creates the mods and config folders.
Note the exact Minecraft version and Forge version your server runs. Both show in the console at startup.

Step by step

Download the mod from CurseForge or Modrinth. Pick the file marked for Forge and your exact Minecraft version.
Check the mod page for required dependencies (library mods it needs) and download those as well.
Check whether it is a server-side mod at all. Client-only mods like shader loaders or minimaps can crash a server. See client-side vs server-side mods.
Stop the server.
In the file manager, open mods and upload the .jar files.
Start the server and watch the console. Forge lists the mods it found while loading.
Install the same mods on your own Forge client and join.

Check the mods loaded

When Forge finishes loading, the server reaches the usual Done line. If a mod is broken, Forge stops with an error before that. Look for lines mentioning the mod's ID, or messages such as:

Missing or unsupported mandatory dependencies:
    Mod ID: 'geckolib', Requested by: 'examplemod', Expected range: '[4.4,)', Actual version: '[MISSING]'

That means a dependency is missing or too old. See mod and version mismatch errors.

Mod configs

Mods put settings in config (and sometimes world/serverconfig or defaultconfigs). Edit them with the file manager while the server is stopped. Files in world/serverconfig apply per world and are sent to clients when they join.

Memory and resources

Mods use much more memory than plugins. A small set of mods may run in 3 to 4 GB, while large packs often need more. Your team's free pool is 6 GB of memory and 10 GB of disk shared across all servers, and you can add more with store upgrades. If the server crashes with out of memory errors, see memory, garbage collection and JVM flags.

Updating or removing mods

To update, stop the server, delete the old jar and upload the new one. Never keep two versions of the same mod.
To remove a mod that adds blocks or items, take a snapshot first. Those blocks disappear from the world, and some worlds fail to load cleanly after a content mod is removed.

Installing a whole modpack?

For a complete pack from CurseForge or Modrinth, use the pack's server files instead of adding mods one by one. See how to install a modpack on a Forge server.

Still stuck?

Post the console error in the Schokr Discord.