Assembly Line Launcher

A custom Minecraft launcher built specifically for the Assembly Line SMP modpack on Modrinth. Supports both cracked (offline) and premium (Microsoft) accounts side by side, auto-updates the modpack from Modrinth, and auto-provisions the correct Java runtime — no manual Java install required.

Built with Python + Qt (PySide6), packaged into standalone executables with Nuitka via GitHub Actions.

Features

• Multi-account: add any number of cracked and Microsoft accounts, switch between them freely.
• Cracked accounts: offline-mode login with vanilla-compatible deterministic UUIDs (same UUID scheme every mainstream launcher uses).
• Premium accounts: real Microsoft sign-in via the OAuth device-code flow (no password ever touches this launcher — you sign in through Microsoft's own page).
• Live modpack sync: fetches the latest version directly from the Modrinth API and asks for confirmation before applying an update.
• Automatic Java provisioning: downloads the correct Eclipse Temurin JRE version for whatever the modpack needs — you never have to install Java yourself.
• Mod loader support: Fabric, Quilt, NeoForge, and Forge.

Getting started (development)

python -m venv .venv
source .venv/bin/activate  # or .venv\Scripts\activate on Windows
pip install -r requirements-dev.txt
python -m launcher.app

Requires Python 3.11+.

Building a standalone executable

pip install -r requirements-dev.txt
python packaging/build.py

The build creates a native installer in dist/: an Inno Setup .exe on Windows, an .AppImage on Linux, and a .dmg on macOS. Linux builds require appimagetool; Windows builds require Inno Setup (ISCC) on PATH. The standalone distribution directory is also kept at dist/AssemblyLineLauncher-<platform>/. Set the LAUNCHER_BUILD_LTO=1 environment variable to enable link-time optimization for a smaller/faster binary at the cost of a much longer build (this is what tagged release builds in CI use).

Pre-built binaries for Windows, macOS, and Linux are published automatically by GitHub Actions on every push, and attached to GitHub Releases for tagged versions (v*).

Project layout

src/launcher/
    auth/       Account models, cracked login, Microsoft OAuth device-code
                flow, account persistence (system keyring when available)
    core/       Modrinth API client, .mrpack installer, vanilla Minecraft
                installer, mod loader installers, Java runtime provisioning,
                instance tracking, launch command building
    ui/         PySide6 GUI: main window, account dialog, settings dialog
    app.py      Entry point
packaging/
    build.py    Nuitka build script
docs/
    MICROSOFT_AUTH_SETUP.md   How to register your own Azure AD app
tests/          pytest test suite (runs in CI on every push)

Microsoft sign-in setup

Premium account login needs an Azure AD client ID. See docs/MICROSOFT_AUTH_SETUP.md for what's currently configured and how to switch to your own.

License

MIT — see LICENSE.