Archie is a Kotlin-first library mod for Fabric and NeoForge, built on Architectury.

It carries the parts every mod ends up writing for itself — screens, config, packets, saved state, storage capabilities — as one set of Kotlin APIs that behave the same on both loaders.

Here because another mod asked for it? Install it alongside and it does its work out of sight.

---

Screens are Compose

Archie runs a real Compose runtime inside Minecraft, so a screen is a function of its state and redraws itself when that state changes.

class MyScreen(menu: MyMenu, inventory: Inventory, title: Component) :
	ComposeContainerScreen<MyMenu>(menu, inventory, title) {
	init { start { content() } }

	@Composable
	fun content() {
		var amount by remember { mutableStateOf(0) }
		ContainerPanel(contentWidth = 18 * 9) {
			Column(verticalArrangement = Arrangement.spacedBy(6)) {
				Label(Component.literal("Amount: $amount"))
				Button(onClick = { amount++ }) { Text(Component.literal("More")) }
				Slots("input")
			}
		}
	}
}

The widget set covers what a machine GUI needs: Text, Icon, Texture, Divider, Spacer, ProgressBar, FluidTank, EnergyBar; Button, Checkbox, Switch, Radio, Slider, Dropdown, ColorPicker, TextField; and containers from Panel and TabContainer through Scrollable, Collapsible, Table, PannableCanvas and a NodeTreeView for graph-shaped data. Dialogs and multi-step Wizard flows come as primitives to build from.

Modifiers chain the way they do in Compose proper — Modifier.size(...).tooltip(...).onScroll { } — and layout is Row/Column/Box with real arrangement and alignment. Anything drawn inside a layer — a modal, a popup editor — participates fully: it takes input first, and it declares its own tooltip without the host screen knowing it exists.

Themes are data. A ComposableTheme names the textures and colours each widget draws with, loaded from resource packs, so a pack restyles every Archie screen at once and a mod ships its own look without forking a widget.

Menus that sync themselves

ComposeBlockContainerMenu pairs a block entity with its screen, and BlockEntityStateManager keeps every field marked @Sync current on the client as it changes. Slots come from real storages — ArchieItemSlot, ArchieFluidSlot, and menu slots backed by Common Storage Lib — so a slot shows what the storage holds.

State that persists itself

NBTHolder gives a block entity or an item stack typed, delegated fields that read and write NBT on their own:

class MyBlockEntity(pos: BlockPos, state: BlockState) : NBTBlockEntity(TYPE, pos, state) {
	@Sync var progress: Int by field(Int.serializer()) { 0 }
	val inventory: ArchieItemStorage by itemField(9)
	val jobs: ObservableList<Job> by listField(Job.serializer()) { emptyList() }
}

Fields nest, so a whole sub-object round-trips as one field. ObservableList and ObservableMap persist every mutation made through them. @Sync marks what the client needs. Data attachments cover state belonging to something you do not own.

Config with a screen for free

A config is a Kotlin object of typed fields. Archie writes the file, generates the Cloth Config screen, and — for a server spec — pushes the values to each client as it joins.

object MyConfig : ConfigContainer(MOD) {
	object Gameplay : ConfigSpec.Server(MOD, Component.literal("Gameplay")) {
		object Machines : CategorySpec(Component.literal("Machines")) {
			var speed by intSlider(
				Component.literal("Speed"),
				Component.literal("Ticks per operation."),
				min = 1, max = 200, default = 20,
			)
		}
	}
}

Fields cover booleans, numbers with or without sliders, strings, enums and arbitrary selectors, colours, keybinds, lists, maps, registry entries, and nested specs.

Packets are data classes

NetworkChannel registers @Serializable Kotlin classes, so a packet is its own wire format.

object MyChannel : NetworkChannel(MOD % "main") {
	fun init() {
		serverbound(SetSpeedPacket::class) { packet, context -> packet.handleOnServer(context) }
		onClient { clientbound(StatusPacket::class) { packet, _ -> packet.handleOnClient() } }
	}
}

Storage and capabilities

One set of item, fluid and energy storages that expose themselves to whichever capability system the loader has: exposeItemStorage, exposeFluidStorage and their siblings take a block entity type and a selector, and the platform difference ends there. Registries, creative tabs and custom model registration work the same way — declare once, get both loaders.

Datagen and GameTest

Two further mods, dev-time only, never on a player's classpath:

• archie-datagen — a Kotlin DSL for models, blockstates, lang, tags, recipes, loot tables and advancements, with builders that read as the JSON they produce.
• archie-gametest — a GameTest harness with assertions, a JUnit bridge, a client-side harness for screens, and screenshot comparison for testing what a GUI actually draws.

Using it

repositories {
	maven("https://maven.kernelpanicsoft.net/releases")
	maven("https://maven.kernelpanicsoft.net/snapshots")
}

dependencies {
	// per loader module
	modApi("net.kernelpanicsoft.archie:archie-core-fabric:<version>")

	// dev-time only
	modCompileOnly("net.kernelpanicsoft.archie:archie-core-gametest-fabric:<version>")
	modLocalRuntime("net.kernelpanicsoft.archie:archie-core-gametest-fabric:<version>")
}

Artifacts are archie-core-{common,fabric,neoforge}, with archie-core-datagen-* and archie-core-gametest-* alongside them.

Full guides live at docs.kernelpanicsoft.net/Archie and in docs/.

---

Requirements

• Minecraft 1.21.1
• Fabric or NeoForge
• Architectury API, Cloth Config — plus Fabric API and Fabric Language Kotlin on Fabric

Status

Pre-release. Everything above is built and in use by Boilerplate, which is what the API is exercised against — so expect it to keep moving where that use finds rough edges.

Bug reports and design arguments are equally welcome on the issue tracker.

Building

One Gradle build at the repo root. Four products - core/ is the library, datagen/ and gametest/ are the dev-time mods above, and test/ is a playground used to exercise Archie during development - each split common/fabric/neoforge and versioned by Stonecutter, so a project path carries the Minecraft version it is for:

./gradlew build
./gradlew :core:fabric:1.21.1:runClient
./gradlew :datagen:neoforge:1.21.1:runDatagen
./gradlew :gametest:fabric:1.21.1:runGametest        # server-side suite
./gradlew :gametest:fabric:1.21.1:runGametestClient  # client GUI harness

Published artifacts keep the flat names the project paths no longer have: archie-core-fabric, archie-core-gametest-neoforge, and so on.

Links

• Source
• Issues
• Documentation

Licensed under GPL-3.0-or-later.