How to make a Fabric Minecraft server with mods

Fabric is a light mod loader. It starts quickly, updates to new Minecraft versions fast, and has a large library of mods on Modrinth. Here is how to run a Fabric server and avoid the usual mistakes.

Mods and plugins are different things

This is the first thing to understand. Plugins (for Paper and Purpur) change the server only. Players join with plain Minecraft. Mods (for Fabric) change the game itself, so they usually have to be installed on the server and on every player's computer. Some mods work server-side only, and the mod page says so.

You cannot mix the two. A Fabric server does not run Paper plugins, and a Paper server does not run Fabric mods. If you want both, pick based on which you need most. The comparison in Paper, Vanilla, Purpur or Fabric can help.

Make the server

On Saryno, press Make a server, choose Fabric as the software and a Minecraft version. Pick a version that your mods support: a mod built for 1.21.4 will not load on 1.21.5. If you have a specific mod in mind, look at its Modrinth page first and choose the newest version it lists. Start with 2 GB. Mods that add many blocks or mobs need more, and big packs need 4 GB or more.

Add Fabric API first

Almost every mod needs Fabric API, a shared library. Open the Mods tab, choose Modrinth and type fabric-api, then press Install. Saryno picks the file made for your Minecraft version.

Add your mods

In the same tab, type the name of a mod from Modrinth, like lithium or ferrite-core, which are popular server-side performance mods. Or upload a jar you downloaded. Restart the game after changes, and read the console: Fabric prints a clear error if a mod is missing a dependency, for example "requires mod fabric-api". The Check for problems button in the Performance tab reads that and tells you.

Make players' game match

For mods that add content, each player needs the same mods and versions. The simplest way is to give them a modpack from Modrinth or a launcher profile. Players on a plain game see "mismatched mod" errors when they try to join.

Mods that make a Fabric server better

These work on the server alone, so players do not need them:

Lithium speeds up game logic
FerriteCore uses less memory
Krypton speeds up networking
spark is a profiler for finding what causes lag

What about Forge and NeoForge?

Forge and NeoForge are different mod loaders with their own mods, and Saryno runs them too: choose one when you make the server. A Forge mod will not load on Fabric, so pick the loader your mods are made for. Quilt runs Fabric mods.

If it will not start

Open the Console and read the first red line.
A mod built for another Minecraft version is the usual cause.
Remove the last mod you added, from the Mods tab, and start again.
Take a backup before you add many mods at once.