Server-Side vs Client-Side Mods: What Actually Needs to Run on the Server

Installing a client-only mod on your server (or vice versa) is one of the most common causes of confusing modded-server startup crashes. Here's how to tell the difference.

Server-Side Mods

These affect actual gameplay logic — world generation, mob behavior, new blocks/items with server-tracked state, dimensions, custom mechanics. These must be installed on the server, and in most cases players need the matching mod installed on their client too, since the mod adds content the vanilla client doesn't know how to render or interact with.

Client-Side Only Mods

These only affect what the player sees or how they interact locally — minimap mods, shader packs, UI/HUD improvements, keybind utilities, visual-only enhancements. Installing these on a server does nothing useful (the server has no rendering to affect) and in some cases can cause the server to crash on startup if the mod assumes a client environment that doesn't exist server-side.

How to Tell Which Is Which

• Check the mod's description/page — most modding platforms (Modrinth, CurseForge) explicitly tag mods as "Client," "Server," or "Client and Server"
• If a mod only changes visuals, UI, or personal quality-of-life with no new gameplay mechanics — it's almost always client-only
• If a mod adds new blocks, items, mobs, or world generation — it's server-side (and usually needed on clients too, to render correctly)

What Happens If You Get It Wrong

• Installing a client-only mod on the server: often causes an immediate crash on startup, since the mod may reference client-only game classes that don't exist in a headless server environment
• Not installing a required server-side mod's client counterpart: players connecting without the mod either can't join at all (version/mod mismatch error) or see broken/missing content

A Practical Rule of Thumb

When in doubt, check the mod page before installing — most modern modding platforms label this clearly, and it takes seconds to confirm versus the time lost troubleshooting a mystery crash afterward.

RepublicNodes' Game Server Hosting supports Forge and NeoForge modded servers with a full file manager for exactly this kind of mod management.