Minecraft
Fabric is a lightweight mod loader. It's quick to update to new Minecraft versions, and it has the best set of performance mods, so it suits both lightly modded survival servers and "vanilla, but faster" servers. Fabric runs Fabric mods only: not Paper plugins, and not Forge or NeoForge mods.
Setup checklist
- [ ] Minecraft version pinned on Startup, with Loader Version on
latest. Versions and Java - [ ] Fabric API in
mods/. Almost every Fabric mod needs it. - [ ] Performance mods installed. Performance mods
- [ ] No client-only mods on the server. Client-only mods
- [ ] Every mod built for your exact Minecraft version.
- [ ] Players given the same mods (for content mods) as a modpack.
- [ ] World pre-generated with Chunky. Pre-generate
- [ ] Backups and a daily restart scheduled. Backup schedules
Memory
| Server | Memory |
|---|---|
| Vanilla-style with performance mods | 3–4 GB |
| 20–50 content mods, 4–8 players | 4–6 GB |
| 50–150 mods, or 10+ players | 6–8 GB |
| Big modpacks (150+ mods) | Follow the pack's own recommendation, usually 8–12 GB |
Leave headroom: the start command gives Java a share of your plan, and the rest is needed outside Java's heap.
Performance mods
These are server-side: players don't need them. Install them from the panel's Minecraft Plugins page or Modrinth, choosing the version for your Minecraft version and Fabric.
| Mod | What it does |
|---|---|
| Lithium | Optimises game logic (mobs, blocks, physics) without changing how the game behaves. Safe on almost any server. |
| FerriteCore | Cuts memory use a lot. |
| C2ME | Faster chunk loading and generation, using more CPU cores. Use release or beta builds, not alpha. |
| ScalableLux | Faster lighting. Replaces the old Starlight mod. |
| Krypton | Lighter networking. |
| ModernFix | Faster start-up and lower memory with many mods. |
| spark | Finds what's causing lag. Fix lag |
| Chunky | Pre-generates the world. |
Check each mod's Modrinth page: the Environments box says whether it's server-side, client-side or needed on both.
Client-only mods crash servers
Mods that change graphics or the screen only work on players' PCs. On a server they crash it during start-up, usually with an error about net.minecraft.client or invalid dist. Never put these on the server:
- Sodium, Iris, Embeddium, Oculus, Rubidium, OptiFine/OptiFabric
- minimaps, HUDs, menus, zoom, sound and shader mods
The crash log names the mod (for example sodium.mixins.json). Delete that jar from mods/ and start again.
Keep versions matched
- Every mod must be built for your exact Minecraft version (
1.21.11isn't1.21.10) and for Fabric. Modrinth's filters do this for you. - When you update Minecraft, update Fabric API and every mod before starting, or remove the ones without an update yet.
- Content mods (new blocks, items, mobs) are needed by players too, at the same versions. Server-side mods aren't.
- The easiest way to give players the same mods: make a modpack in the Modrinth app or Prism Launcher and share it. Install mods and modpacks
Restarts and backups
- A daily restart at a quiet time, with warnings. Heavily modded servers do better with one every 12 hours.
- Backups every 6 hours, with
save-allfirst, and a locked backup before adding, removing or updating mods. Removing a content mod deletes its blocks and items from the world.
Running behind Velocity
Fabric servers in a Velocity network need FabricProxy-Lite for secure forwarding. There's no supported Fabric mod for Velocity's legacy (BungeeCord-style) forwarding, so use modern forwarding.
Security
online-mode=true, a whitelist for private servers, few ops. Players- For permissions, use LuckPerms (Fabric); for grief logging and rollbacks, Ledger.
enable-rcon=false.
Common problems
| Problem | Fix |
|---|---|
Crash mentioning net.minecraft.client or a mod's mixins |
A client-only mod is installed. Delete it. |
| Mod X requires fabric-api | Install Fabric API for your Minecraft version. |
| Incompatible mod set / version errors | A mod is for a different Minecraft version. Get the right version or remove it. |
| Players kicked with mod mismatch / missing registry entries | They're missing a content mod, or have a different version. Share the modpack. |
| Strange errors after updating the loader | Ask us to clear the old .fabric cache folder, or delete it with the server stopped. |