Client & Server

Minecraft runs in two environments: Client and Server. Understanding the difference is important for modding.

The two sides

Side	What it runs	What it does
Client	Your computer	Renders graphics, plays sounds, handles input
Server	The game world	Runs game logic, manages entities, saves data

In singleplayer, both run on your computer but stay logically separate. In multiplayer, you run the Client and connect to a separate Server.

Why this matters

Some code should only run on one side:

Code	Side	Reason
Register items/blocks	Both	Both sides need to know about them
Render a custom model	Client only	Servers do not render graphics
Save player data	Server only	Only the server saves data
Open a GUI	Client only	Only the client shows screens

Script folders

FoundryEngine organizes scripts into three folders matching these sides:

scripts/
├── common/my_bundle/     # Runs everywhere
├── client/my_bundle/     # Runs only on the client
└── server/my_bundle/     # Runs only on the server

Entrypoints per side

Each folder can have its own entrypoint. You do not need all three — only the ones your bundle needs:

// scripts/common/my_bundle/Entrypoint.groovy
class Entrypoint implements BundleEntrypoint {
    @Override void onLoad() {
        // Register items, blocks, recipes — runs everywhere
    }
}

// scripts/client/my_bundle/ClientEntrypoint.groovy
class ClientEntrypoint implements BundleEntrypoint {
    @Override void onLoad() {
        // Client-only setup — renderer hooks, keybinds
    }
}

// scripts/server/my_bundle/ServerEntrypoint.groovy
class ServerEntrypoint implements BundleEntrypoint {
    @Override void onLoad() {
        // Server-only setup — commands, data
    }
}

Quick reference

What you want to do	Put it in
Create items, blocks, recipes	common/
React to player join, block break	common/
Custom rendering, particles	client/
GUI, key bindings	client/
Server commands	server/
Save/load data	server/ or common/

Next

• Scripts — writing scripts for each side
• Events Guide — some events are side-specific