Project Structure

An Architectury mod is split into subprojects - one shared module plus one per loader you target. Understanding what belongs where is the key to working productively.

The subprojects

Subproject	Contains
common	Your actual mod logic, written against the common API. This is the bulk of your code.
fabric	The Fabric entrypoint and any Fabric-only implementations.
neoforge	The NeoForge entrypoint and any NeoForge-only implementations.

The goal is to put as much as possible in common and keep the platform modules thin - ideally just the loader entrypoint that calls into your common initializer.

my-mod/
├── common/      -> shared code + shared resources 
├── fabric/      -> Fabric entrypoint (fabric.mod.json + initializer)
└── neoforge/    -> NeoForge entrypoint (neoforge.mods.toml + initializer)

Where your code goes

Write your features in common using the Architectury API. For example, registering an item or listening to an event is done once in common and works on both loaders:

common/.../MyMod.java

public final class MyMod {
    public static final String MOD_ID = "mymod";

    // Runs from both the Fabric and NeoForge entrypoints.
    public static void init() {
        PlayerEvent.PLAYER_JOIN.register(player -> {
            player.sendSystemMessage(Component.literal("Welcome to my mod!"));
        });
    }
}

Each platform module then has a tiny entrypoint that calls MyMod.init():

fabric/.../MyModFabric.java

public final class MyModFabric implements ModInitializer {
    @Override
    public void onInitialize() {
        MyMod.init();
    }
}

neoforge/.../MyModNeoForge.java

@Mod(MyMod.MOD_ID)
public final class MyModNeoForge {
    public MyModNeoForge() {
        MyMod.init();
    }
}

Building and running

From the project root, use the Gradle wrapper:

# Build every platform jar (outputs to fabric/build/libs and neoforge/build/libs)
./gradlew build

# Launch a development client for a specific loader
./gradlew :fabric:runClient
./gradlew :neoforge:runClient

# Launch a dedicated server
./gradlew :fabric:runServer
./gradlew :neoforge:runServer

Build outputs

The finished, distributable jars are the ones in common/build/libs, fabric/build/libs and neoforge/build/libs (the files without the -dev or -sources suffix).