A modded server only works when the server and every player run the same mod loader, the same mods and the same versions. For a friend group, the easiest route is a modpack: install the pack on the server, then have everyone install the identical pack in a launcher that supports it.
Most “my mods don’t work on the server” problems are a mismatch, not a bug. This guide covers the setup in the order that avoids them. If you have not picked a loader yet, start with Fabric vs Forge vs NeoForge. If you only want server-side features like land claims or homes, plugins may be enough; see plugins vs mods.
Mods vs a modpack: which to add
- A modpack is a curated set of mods, configs and a fixed loader version. Install it once on the server and once per player, and everything matches by design. Best for most friend groups.
- Individual mods let you build your own set, but you have to keep the loader, Minecraft version and every mod’s version in step yourself, plus any dependency mods.
Some mods are client-only (minimaps, shaders, performance mods). Players can add those to their own game without the server needing them.
How to add mods to a Minecraft server
- Pick the loader and Minecraft version. The server software must be the loader, for example a Fabric or NeoForge server, not plain vanilla or Paper.
- Add the server-side mod files for that exact loader and version, including any library mods they depend on.
- Start the server once and read the log. A missing dependency or wrong version usually names the mod that caused it.
- Give players the same set. Each player installs the same loader and mods; client-only extras are optional.
Start with a fresh world or a backup. Adding mods that change world generation to an existing world can leave odd chunk borders, and removing a mod can delete the blocks and items it added. Our backup guide covers making a copy first.
How to add mods and modpacks on Aternos
Aternos works from a curated library rather than file uploads:
- Individual mods: pick a mod-capable server software (Aternos names Forge as the most common, with Fabric as an alternative), then add mods from its mod library, which draws on CurseForge and Modrinth. You cannot upload mod files you downloaded yourself. Some mods need dependencies, which you may have to look up on the mod’s own page.
- Modpacks: choose the pack in the server’s software section. Aternos supports packs from CurseForge, Modrinth, ATLauncher and the FTB App, one at a time, and you cannot change the individual mods inside a pack.
- A pack that isn’t listed: Aternos takes suggestions. A pack needs server files to be added; Modrinth and ATLauncher packs always have them, CurseForge packs vary.
Then every friend installs the same pack and version in the matching launcher, such as the Modrinth App or the CurseForge App, and joins the server address.
Give your friends the same setup
The cleanest way is a launcher profile everyone installs from the same source:
- Modpack: share the pack’s name and exact version. Everyone installs it in the launcher it comes from (Modrinth App, CurseForge App, Prism Launcher or similar).
- Custom mod list: export your launcher profile, or share a list with exact file versions. “Latest” is not a version.
When someone gets a “mismatched mods” or “missing mods” message on joining, compare their mod list with the server’s. It is almost always one version off.
How much RAM does a modded server need?
Mods and modpacks need more memory than vanilla, and big packs with world generation or tech mods need much more. Look at the pack’s own recommendation first, then size by how many people play at once. Our RAM guide covers the numbers; if the server stutters anyway, see fixing lag and low TPS.
Play modded Minecraft with friends without a server
For a quick session you can skip the server: load the modded singleplayer world and use Open to LAN. Everyone needs the same mods. The world only runs while the host plays, and friends outside your home network need extra tools to reach it, so a server is easier once a group plays regularly.
Checklist
- Same Minecraft version and loader on the server and every player.
- Server-side mods plus their dependencies installed, log checked.
- A backup or fresh world before adding world-generation mods.
- Every player on the identical modpack or mod list.
- Enough RAM for the pack and the group size.