Server Setup

How to Install a Fabric Server

Fabric is the fast, light way to run a modded Minecraft server. Download the launcher, drop in Fabric API plus a couple of performance mods, and you get a snappy server that boots in seconds with Loading N mods ... done in the console.

fabric-server, bash, 80×24
$ java -jar fabric-server-launch.jar nogui
[main/INFO] Loading Minecraft 1.21.4 with Fabric Loader 0.16.10
[FabricLoader] Discovering mods in mods/ ...
 + fabric-api 0.115.0   + lithium 0.14.7   + ferritecore 7.0.0
[main/INFO] Loading 4 mods ......... done
[Server thread] Preparing level "world"
[Server thread/INFO] Preparing spawn area: 0%
[Server thread/INFO] Done (5.812s)! For help, type "help"
Steve joined the game
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Why mods go in mods/

Fabric Loader scans the mods/ folder at boot and resolves dependencies in order, which is why fabric-api must be present before anything that needs it. Keep server-side-only mods (Lithium, FerriteCore, spark) here so vanilla clients can still connect, and put any content mods on both the server and every player.

Quick answers

What is the difference between Fabric and Forge?

Fabric is a lightweight modloader that updates fast and runs lean; Forge is heavier with deeper API hooks. Mods are not cross-compatible, so pick the one your mods target.

Do I always need Fabric API?

Almost. Most Fabric mods depend on fabric-api for shared hooks. Install it first or those mods fail to load with a "missing dependency" error in console.

Why won't my server start?

Common causes: eula not set to true, a Java version mismatch (1.21 needs Java 21), or a mod built for a different Minecraft version. Read the first red line in the log.

How much RAM should I give it?

2-4GB is fine for a small vanilla-plus Fabric server. Set it with -Xmx4G -Xms4G in your start command. Add more only as players and mods grow.

Can players use a vanilla client?

Only if every installed mod is server-side (Lithium, FerriteCore, spark). Any mod that adds blocks or items means players must run Fabric with the same mods.

Where do I set the world and player limit?

In server.properties, generated on first run. Edit level-name, max-players, gamemode and difficulty, then restart for the changes to apply.

The loader, the API and the version lock

The server jar and the loader are two different downloads

Fabric gives you a launcher that pulls the loader, and the game server itself still has to be there. Running the loader against a missing or mismatched server jar is the usual first failure, and the log says so plainly in its first ten lines.

Most mods need Fabric API as well

Fabric API is a separate mod file, not part of the loader, and a mod list that quietly does nothing on startup is usually a missing API. Install it first and update it at the same time you update the loader, because a stale API breaks mods that did not change.

Every mod is locked to one game version

A mod built for one version will refuse to load on the next, so upgrading the server means checking every mod before the upgrade rather than after. Keep the working mods folder as a copy before you touch anything, because rolling back a world is much harder than rolling back a folder.