Minecraft Server with Slimefun: Which Version to Pick, How to Install It and Addons

What Slimefun is

A plugin for Paper (or Spigot) servers that adds hundreds of new items: machines that run on electricity, solar panels, backpacks, special armour, talismans, robots (the Androids), an item transport system (Cargo) and much more. It feels like playing a tech modpack, but without mods: everything is made from normal blocks and items of the game with another name and another texture in the inventory.

That's why people love it so much: every player joins with their Minecraft without touching anything, and the rest of the server's plugins (protection, permissions, economy) keep working. Each item is unlocked with “researches” that cost experience levels, and the Slimefun guide (a book you get when you join) shows the recipe for everything.

The version: the most important thing before you start

The official Slimefun (the one from the Slimefun team, on GitHub) says it works from 1.16 to 1.20. Today it doesn't publish a build for 1.21 or for 26.x, which is the version new servers start on. If you put it on the latest version of Paper, the usual result is that it doesn't load or fails now and then.

For the new versions there are forks made by the community (on Hangar and Modrinth they come up when you search for “Slimefun”): copies of the original brought up to date by other people. Some work well, but they aren't from the Slimefun team, several are marked as “experimental” and the addons don't always work with them. If you use one, read which versions it says it supports and test before opening the server to your group.

In short: if you want stability and the well-known addons working, set the server up on 1.20 (1.20.6 is the last of that branch) with the official Slimefun. If being on the latest version matters more to you than stability, a fork, knowing what it is.

Installing it on your PC

For friends outside your home to join, you'll have to open port 25565 on your router and leave the PC on while they play.

1. Paper in the right version

   Download Paper from papermc.io in the version you chose (for example, 1.20.6 from its older versions). 1.20.5 and 1.20.6 need Java 21; 1.17 to 1.20.4, Java 17.

2. Start it once

   Accept the EULA (eula=true in eula.txt), start it again and stop it once it has created its folders.

3. Download Slimefun

   From the download site linked on its GitHub page (Slimefun/Slimefun4). Its own authors recommend the “Dev” builds over the “stable” ones, which they say are very out of date.

4. Into the plugins folder

   Put the Slimefun .jar (and whatever addons you want) in the plugins folder and start the server. When they join, each player gets the Slimefun guide.

How it's done at NapNodes

Minecraft servers start on Paper in the latest version. For the official Slimefun, switch it to 1.20 from the panel: “Mods & plugins” → “Server type” tab, choose Paper and the version from the list (it comes from Paper). The panel sets Java by itself: you don't have to touch anything Java-related. This works on the free server too.

The panel won't let you downgrade with a world in place, because a world created in a newer version breaks in an older one. If the server already has a world, move it aside first (in “Files”, rename the world folder) and a new one will be created on 1.20.

The official Slimefun isn't on Modrinth or CurseForge: you download it from its website and upload it in “Files”, inside the plugins folder. Forks that are on Modrinth may show up in the plugins tab of “Mods & plugins”, which only shows the ones that work with your version.

1. Make a backup

   In “Backups”, if there's a world you want to keep. The free server has no backups: in “Files”, compress the world folder and download it.

2. Move the current world aside

   In “Files”, rename the world folder (for example, to world-before). If the server is new, skip this step.

3. Pick Paper 1.20.6

   In “Mods & plugins” → “Server type”, click Paper, choose 1.20.6 from the list and “Change”. It takes a few minutes and the panel tells you when it's done.

4. Upload Slimefun

   In “Files” → plugins, upload the Slimefun .jar and those of its addons. Then “Restart”.

5. Check the console

   The “Console” should show Slimefun loaded with no errors. Join, type /sf versions and you'll see Slimefun and each addon with its version.

Addons: the most popular ones

Slimefun has a list of addons on its wiki. Among the best known: ExoticGarden (plants, trees and food), InfinityExpansion (endgame machines and recipes), FluffyMachines (more machines and generators), Galactifun (planets and rockets), Networks (networked storage, in the style of storage mods) and SlimeTinker (tools built from parts).

Each addon is another .jar in the plugins folder and depends on Slimefun: it has to match the same Slimefun and Minecraft version as the server. The wiki itself warns that community addons may be out of date. Add them one at a time and check the console after each one: if something doesn't load, you'll know which one it was.

Slimefun commands

They all start with /sf (or /slimefun). For players: /sf guide (gives you the guide again), /sf search <word> (searches for an item in the guide), /sf stats and /sf help.

For admins: /sf cheat opens a menu with every item (click and you get it), /sf give <player> <item> [amount] gives a specific item, /sf research <player> all unlocks every research (or reset to remove them), /sf timings shows which machines are using the most server time and /sf versions lists Slimefun and its addons.

The admin ones need permissions (for example, slimefun.cheat.items for /sf cheat and /sf give). If you're OP you have them; if you use ranks with LuckPerms, give them only to the admin rank.

Settings people usually change

They're in plugins/Slimefun: config.yml (general options, like the language or whether the guide is given on join) and Researches.yml, where you change how many levels each research costs or turn researches off entirely (everything unlocked from the start, handy on a friends' server that wants to move fast).

Change these files with the server stopped and start it afterwards. Don't use /reload with Slimefun: its own authors warn that it causes problems.

Slimefun is translated into many languages, Spanish included: the language is chosen in config.yml.

How much RAM and CPU it needs

Slimefun on its own doesn't use much more than a survival server with plugins: for a group of friends on 1.20, 4 GB is fine, and the free server is enough to try it out. With lots of big addons (InfinityExpansion, Networks) or more than 10 players, better 6 GB.

What really weighs is the CPU once people build factories: every machine, generator and Cargo network works every few ticks, and with hundreds at once the server struggles even with RAM to spare. /sf timings tells you what's using the most; limiting how many machines each player (or each chunk) can place is what works best. At NapNodes your plan's RAM and CPU are yours alone, with no overselling: you don't compete with other servers' factories.

Common problems

Slimefun doesn't load and the console says the version isn't supported: you're on a newer Minecraft version than your Slimefun supports. Switch the server to 1.20 (moving the world aside) or look for a fork for your version.

“UnsupportedClassVersionError” on startup: the plugin is built for a newer Java than the server's. On 1.20.4 or earlier (Java 17), plugins built for Java 21 don't load. Check the plugin's version or use 1.20.6.

One addon throws errors and the rest work fine: it's almost always not built for your Slimefun version. Remove it from the plugins folder, “Restart”, and find the right version.

The server stutters when people have factories running: it's CPU, not RAM. Use /sf timings to see what it is and limit machines, or a bigger plan if the group grows.

Frequently asked questions