Mods · 15 min
Understand client-side, server-side, and required-on-both mods
Decide where a mod belongs before installing it so clients can connect, servers can start, and single-player instances stay clean.
What you will accomplish
Decide where a mod belongs before installing it so clients can connect, servers can start, and single-player instances stay clean. The goal is a repeatable result you can verify, not a pile of unexplained files.
- Project side is documented
- Dependencies are installed on the correct side
- Client and server versions match when required
- Optional client mods do not change shared content
Three practical categories
Client-only projects change rendering, controls, menus, sounds, maps, or other local presentation without adding shared blocks or mechanics. Server-only projects change rules or administration while allowing unmodified clients to connect. Required-on-both projects add shared content, registries, packets, or gameplay systems that both sides must understand.
These labels are practical descriptions, not perfect technical guarantees. Always defer to the project documentation and test the exact version you plan to use.
Build a clean server pack
Start with the loader and required shared mods. Add server-only utilities next. Leave visual, shader, keybind, screenshot, and most HUD projects out unless their documentation explicitly supports dedicated servers.
A smaller server mod folder starts faster, uses less memory, and creates fewer opportunities for environment-specific crashes.
Publish clear player requirements
Tell players which loader version, modpack version, and optional client improvements are supported. If a project is required on both sides, include its exact version in the manifest. Clear requirements reduce support requests and prevent players from downloading random “close enough” versions.
How to know you are finished
For understand client-side, server-side, and required-on-both mods, the work is not finished when a file is merely downloaded. Treat it as finished when you can point to the setup you changed, explain why it matches the intended Minecraft version or platform, and repeat the result in a clean test or copied world.
Use the checklist as the exit test: project side is documented, dependencies are installed on the correct side, client and server versions match when required. If one of those checks is still uncertain, stop and verify that detail before moving to a main world, public server, or shared pack.
If the first failure you hit is "The server crashes during startup", start with this fix: Remove client-only rendering, UI, shader, or input mods from the server and check the first meaningful error in the server log. This keeps recovery tied to the guide instead of turning into unrelated guesswork.
Step-by-step process
Read the project side labels and description before downloading
Read the project side labels and description before downloading.
Identify whether the mod changes only presentation, only serv...
Identify whether the mod changes only presentation, only server behavior, or shared game content and networking.
For a dedicated server, make a separate server instance rathe...
For a dedicated server, make a separate server instance rather than copying the entire client mods folder.
Test connection with one clean client and review both client...
Test connection with one clean client and review both client and server logs.
Document which projects are required, optional, or prohibited...
Document which projects are required, optional, or prohibited for players.
Verification checklist
Project side is documented
Dependencies are installed on the correct side
Client and server versions match when required
Optional client mods do not change shared content
A clean connection test succeeds
Server pack instructions are written down
Troubleshooting
Remove client-only rendering, UI, shader, or input mods from the server and check the first meaningful error in the server log.
Compare project versions and required dependencies on both sides. Shared content mods normally need matching installations.
The server may enforce a mod list or the project may not be fully client-only. Check its networking and compatibility notes.
Practical notes
- “Works on a server” is not the same as “must be installed on the server.”
- Single-player uses an integrated server, so some server-side behavior still matters.
- Maintain separate client and server manifests for modpacks.
Official-source standard
FreeMinecraftMods does not mirror project files. When this guide involves a download, verify the creator, version, loader, file availability, license, and final official source before installing anything.
Read how project listings are reviewed or report a correction.