Brass & Sigil Launcher
A private custom Minecraft Java Edition launcher built for distributing a personal modpack (Create, aeronautics, tech and magic, with Distant Horizons) to a small friend group. Built in C# / .NET 8 / Avalonia, ships as a single self-contained Windows executable.
About the project
Brass & Sigil is a private Minecraft modpack centred on the Create mod, aeronautics, tech and magic mods, with Distant Horizons for far-render exploration. This launcher is the desktop client built specifically to distribute the pack to a small friend group (under 50 players, no public release).
The launcher is a native Windows application written in C# on .NET 8, using the Avalonia UI framework. It ships as a single self-contained executable so friends can just download and run it — no installer, no .NET runtime to install, no separate config files.
What it does
- Fetches a JSON manifest from a self-hosted server and syncs the modpack files (mods, configs, resourcepacks) to the player's local install directory, using SHA-1 hashing so only changed files are downloaded.
- Authenticates the player with their own personal Microsoft account via the standard MSAL OAuth flow, so only legitimate Minecraft Java Edition owners can sign in.
- Installs the right Minecraft version and Forge loader, then launches the game with the configured memory and the player's session.
- Auto-updates the modpack on every launch when the manifest changes — players never have to manually install or update mods.
Technical details
Language: C# (.NET 8)
UI Framework: Avalonia 12
Minecraft auth: CmlLib.Core.Auth.Microsoft
Game launching: CmlLib.Core 4.x + Forge installer
Distribution: Single-file self-contained .exe
Audience: Private friend group (< 50)
Privacy & data
The launcher does not collect, store, or transmit any user data beyond what the standard Microsoft and Minecraft authentication flows require. Auth tokens are cached locally on the player's machine via the MSAL token cache — no telemetry, no analytics, no third-party services beyond Microsoft and Mojang.
The modpack manifest and mod files are served from a self-hosted Linux server that I personally operate.
Status
Active development. The launcher is functional end-to-end (manifest sync, Microsoft auth, Forge install, game launch) and is currently being prepared for distribution to a small group of friends.
NOT AN OFFICIAL MINECRAFT PRODUCT. NOT APPROVED BY OR ASSOCIATED WITH MOJANG OR MICROSOFT.