Getting started

This page takes you from an empty mod to a working custom power type. You should already have a Fabric (or NeoForge) mod project building.

1. Depend on Apoli#

In build.gradle, add Apoli. The coordinate is qualified by loader and Minecraft version:

repositories {
    mavenLocal() // if you build Apoli yourself
}

dependencies {
    modImplementation "dev.overgrown:apoli-fabric-1.21.1:${apoli_version}"
}

And declare the dependency in fabric.mod.json so the game enforces it:

{ "depends": { "apoli": ">=1.5.0" } }

2. An id helper#

Everything you register needs an id in your namespace. Mirror Apoli’s helper:

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

    public static ResourceLocation id(String path) {
        return ResourceLocation.fromNamespaceAndPath(MOD_ID, path);
    }
}

3. Write a power type#

A power type is a PowerType<C> where C is a config record. The codec is the JSON schema:

public final class GravityPower extends PowerType<GravityPower.Cfg> {
    public record Cfg(double multiplier) {}

    private static final MapCodec<Cfg> CODEC = RecordCodecBuilder.mapCodec(i -> i.group(
        Codec.DOUBLE.optionalFieldOf("multiplier", 1.0).forGetter(Cfg::multiplier)
    ).apply(i, Cfg::new));

    @Override public MapCodec<Cfg> configCodec() { return CODEC; }

    @Override public void onAdded(ResourceLocation id, Cfg cfg, PowerContainer holder, ResourceLocation source) {
        // apply the effect to holder.owner()
    }
}

See Registering power types for the full lifecycle.

4. Register it#

During mod initialisation (your entrypoint), hand it to the registry:

public class MyModInit implements ModInitializer {
    @Override public void onInitialize() {
        PowerTypeRegistry.register(MyMod.id("gravity"), new GravityPower());
    }
}

5. Use it from JSON#

Your type is now a first-class Apoli type — any data pack (including yours) can write:

{ "type": "mymod:gravity", "multiplier": 0.4 }

Where things get registered#

You’re adding…	Register with
a power type	PowerTypeRegistry.register
an action	ActionTypes.ENTITY / .BI_ENTITY / …
a condition	ConditionTypes.ENTITY / …
a reusable JSON value type	a shared Codec

Next#

• Registering power types
• Actions & conditions
• Performance rules — read before shipping tick code.