Developer API

ViaFabricPlus exposes events and utility functions so other mods can integrate with it. If you want to include it in your project, keep in mind:

• Requires Java 17
• Needs a Fabric Loom setup (since it's a Minecraft mod, not a standalone API library)

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Adding as a Dependency

If you only need the public API, include the viafabricplus-api artifact. If you also want to access internal features (including the legacy compatibility layer), use viafabricplus.

Kotlin (Gradle)

repositories {
    // https://github.com/ViaVersion/ViaFabricPlus/blob/ver/<version>/docs/DEVELOPER_API.md
    maven("https://repo.viaversion.com")
    maven("https://maven.lenni0451.net/everything")
    maven("https://maven.terraformersmc.com/releases")
    maven("https://jitpack.io") {
        content {
            includeGroup("com.github.oryxel1")
        }
    }
}

dependencies {
    // Replace it with latest release
    runtimeOnly("com.viaversion:viafabricplus:x.x.x")
    compileOnly("com.viaversion:viafabricplus-api:x.x.x")
}

Groovy (Gradle)

repositories {
    mavenCentral()
    maven { name = "ViaVersion"; url = "https://repo.viaversion.com" }
    maven { name = "Lenni0451"; url = "https://maven.lenni0451.net/everything" }
    maven {
        name = "Jitpack"
        url = "https://jitpack.io"
        content { includeGroup "com.github.oryxel1" }
    }
}

dependencies {
    // Replace it with latest release
    runtimeOnly("com.viaversion:viafabricplus:x.x.x")
    compileOnly("com.viaversion:viafabricplus-api:x.x.x")
}

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Using the API

Get the main API instance with:

final ViaFabricPlusBase platform = ViaFabricPlus.getImpl();

The ViaFabricPlusBase interface contains all stable API functions that other mods can safely use.

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Event Callbacks

ViaFabricPlus provides two key callbacks:

• LoadingCycleCallback – Fired at different stages of ViaFabricPlus loading (config, settings, files, etc.)
• ChangeProtocolVersionCallback – Fired when the user switches to another protocol version (manually or by joining a server)

Example: Listening for version changes

final ViaFabricPlusBase platform = ViaFabricPlus.getImpl();

platform.registerOnChangeProtocolVersionCallback((oldVersion, newVersion) -> {
    // Called whenever the target protocol version changes
});

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Loading Cycle Callback

Since your mod may load after ViaFabricPlus, you need to register callbacks inside a ViaFabricPlusLoadEntrypoint declared in your fabric.mod.json as viafabricplus. This entrypoint also represents the INITIAL_LOAD stage.

public class Example implements ViaFabricPlusLoadEntrypoint {

    @Override
    public void onPlatformLoad(ViaFabricPlusBase platform) {
        platform.registerLoadingCycleCallback(stage -> {
            if (stage == LoadingCycleCallback.LoadingCycle.PRE_SETTINGS_LOAD) {
                // Before settings are loaded
            } else if (stage == LoadingCycleCallback.LoadingCycle.POST_SETTINGS_LOAD) {
                // After settings are loaded
            } else if (stage == LoadingCycleCallback.LoadingCycle.PRE_FILES_LOAD) {
                // Before files are loaded
            } else if (stage == LoadingCycleCallback.LoadingCycle.POST_FILES_LOAD) {
                // After files are loaded
            } else if (stage == LoadingCycleCallback.LoadingCycle.PRE_VIAVERSION_LOAD) {
                // Before ViaVersion initializes
            } else if (stage == LoadingCycleCallback.LoadingCycle.POST_VIAVERSION_LOAD) {
                // After ViaVersion initializes
            } else if (stage == LoadingCycleCallback.LoadingCycle.FINAL_LOAD) {
                // After everything is fully loaded
            } else if (stage == LoadingCycleCallback.LoadingCycle.POST_GAME_LOAD) {
                // After the game finishes loading
            }
        });
    }
}

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Extended API

For version-specific tasks, ViaFabricPlus provides a range of helper methods. Since it relies on ViaVersion, you can also use the ViaVersion API directly.

Example: Get current protocol version

final ProtocolVersion version = ViaFabricPlus.getImpl().getTargetVersion();