A client-only mod stops your Minecraft server

Some mods are made only for the game a player runs on their computer, not for a server. They change what the player sees, such as graphics or menus, and a server has no screen. Put one in the server's mods folder and Fabric, Forge or NeoForge stops at start. Turn that mod off on the server. Players can keep it in their own game.

What you see

The Why your server stopped box on Overview and above the Console says the mod's name and only runs in the game, not on a server., then Remove it from the server's mods folder. Players can still use it in their own game.

The button is one of these:

• Turn this mod off, when the panel read the mod's file name from a crash report. One click turns it off.
• Open in Files, when the cause came from the console, or the file name was not found. It opens the mods folder, where you turn it off yourself.

In the Console or the crash report:

• Forge and NeoForge: Attempted to load class and a class name, then for invalid dist and the server's name for itself.
• Fabric: Cannot load class and a class name in environment type SERVER.

A crash report often names the file just above, on a line starting Mod File:.

Turn it off in one click

1. Open your server in the panel, on Overview or Console.
2. In Why your server stopped, click Turn this mod off. The panel renames the file so it ends in .disabled, and says it is turned off. Start the server again.
3. Click Start.

Turn it off by hand

Either way works:

• On Modding, open Mods, then Installed, and use the switch on the mod's row to switch it off.
• In Files, open the mods folder, find the mod's file (its name is usually close to the mod's name in the message), and delete it or rename it so it ends in .disabled.

Then start the server. If another mod is named, do the same for it.

How to tell before you install

A mod's own page says whether it is for the client, the server or both. When you put mods on a server by hand, for example from a modpack you play with, leave out the ones made only for the player's game. Installing from Modding is covered in How to install mods on Forge, Fabric and NeoForge.

Good to know

• Turning a mod off keeps the file. To turn it back on, remove .disabled from its name in Files.
• Other causes the panel names: How to see why your Minecraft server stopped.