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 that builds.

1. Depend on Apoli

In build.gradle, add Apoli. Its version string names the loader and Minecraft version, such as 1.118.1+1.21.1-fabric:

repositories {
    mavenLocal()
}

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

mavenLocal() is for an Apoli you build and publish yourself with its publishToMavenLocal task. Released builds come from the Modrinth Maven repository, https://api.modrinth.com/maven, as maven.modrinth:opoli:<version>. On NeoForge, use implementation instead of modImplementation.

Then 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 own namespace. A small helper like Apoli's keeps that in one place:

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, and its 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; }
}

To make it do something, override onAdded and apply the effect to holder.owner(), along with whichever other lifecycle hooks you need. See Registering power types for the full lifecycle.

4. Register it

During mod initialisation, in 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 an Apoli type like any other, and any data pack, including yours, can use it:

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

Where things get registered

Next

• Registering power types
• Actions and conditions
• Performance rules, to read before shipping tick code