Client-side vs server-side mods: which go on the server?
Learn which Minecraft mods belong on the server, which only on the client, and how to fix crashes caused by client-only mods on a Forge server.
Updated · 2 min read
Mods that add content (blocks, items, mobs, dimensions, machines) must be on both the server and every player's client. Mods that only change visuals, the HUD or your controls are client-side only and should not be uploaded to the server.
The three kinds of mods
| Kind | Install on | Examples |
|---|---|---|
| Both sides | Server and every client | New blocks, items, mobs, biomes, tech and magic mods, and the libraries they need. |
| Client only | Players' computers only | Shader and rendering mods, minimaps, HUD and inventory tweaks, zoom, sound and visual effects, FPS boosters, OptiFine. |
| Server only | Server only | Admin tools, performance tweaks that run on the server, backup or chunk pre-generation mods, some anti-grief mods. |
Some mods work in either place. For example, recipe viewers and some quality-of-life mods are optional on the server but add features when present on both sides. The mod page usually says "client", "server" or "both". Modrinth shows this on each project page.
Why client-only mods crash servers
A dedicated server does not include Minecraft's rendering code. When a client-only mod tries to load it, the server stops with an error like:
Attempted to load class net/minecraft/client/Minecraft for invalid dist DEDICATED_SERVER
or a NoClassDefFoundError mentioning net/minecraft/client. Anything mentioning client in the crash and naming a mod is a strong sign that mod is client-only.
Fix
- Read the crash report or console to find the mod name or mod ID in the stack trace.
- Stop the server and delete that jar from
mods. - Start the server again. Repeat if another client mod causes the next crash.
If the stack trace does not name the mod, remove recently added mods one at a time (or half at a time) until the server starts.
Modpacks and client mods
Modpacks are built for players, so the full client pack often includes client-only mods. That is why pack authors publish separate server files with those mods already removed. Always use the server pack when one exists. See how to install a modpack on a Forge server.
If you build a server from the client pack yourself, go through the mods folder and remove the visual, HUD and performance-only client mods before starting.
What players need
- Every both sides mod, at the exact same version as the server.
- Any client only mods they like. These are up to each player and do not need to match.
- They should not need any server only mods.
If players cannot join because of differences, see mod and version mismatch errors.