Vesper Launcher

A Minecraft: Java Edition launcher with its own client mod, a built-in server manager, and a theme system that actually recolours everything.

Mauve on black by default. Every colour is yours to change.

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What this is

Vesper is a desktop launcher for Minecraft: Java Edition. It downloads and runs any version Mojang has ever published, installs mod loaders for you, and keeps every instance isolated so your worlds and mods never collide.

It goes further than a plain launcher in three ways:

• Vesper Loader is our own curated profile, built on Fabric or Forge, that ships a client mod we write ourselves. Motion blur, a configurable HUD, cosmetics, and a performance bundle, all in one click.
• Servers are first-class. Spin up a Paper or Purpur server, watch its console, manage plugins, and expose it to friends over a playit.gg tunnel without touching your router.
• Themes are data, not code. Every brush in the app binds to a token, so a theme file recolours the entire interface at runtime with no restart.

Nothing is written to your .minecraft folder. Vesper keeps its own directory.

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Features

	Feature	Notes
Versions	Every Mojang release	Releases, snapshots, betas, alphas, all the way back
Loaders	Fabric, Forge, NeoForge, Quilt	Pick the loader and the loader version, not just latest
OptiFine	Manual import	Its licence forbids redistribution, so you supply the jar and Vesper runs the installer
Vesper Loader	Fabric or NeoForge, 1.21+	Our mod plus a curated performance bundle, installed in one click
Accounts	Microsoft and local	Local accounts need no Microsoft account and have no restrictions
Skins	Change skins for both	Real API calls for Microsoft accounts, mod-driven rendering for local ones
Servers	Paper and Purpur	Start, stop, restart, live console, plugins, playit.gg tunnel
Java	Managed automatically	The right JRE per version, downloaded for you. Java 8 for old versions, 21 for modern
Mods	Modrinth and CurseForge	Browse and install in-app, or drop jars in the folder and rescan for metadata
Skins	3D editor built in	Rotate the model, paint pixels directly onto it, upload a PNG, save per account
Isolation	Per-profile game directories	Shared libraries and assets, so twenty profiles do not mean twenty copies
Themes	Fully tokenised	Change any colour in the app, live

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Accounts

Vesper supports two account types, and either one can be created first on a fresh install.

Local accounts ask for a username and nothing else. No password, no validation, no Microsoft account required, no restrictions on the name. They use the standard offline UUID derivation (OfflinePlayer:<name> hashed to a version-3 UUID), which is byte-for-byte identical to what the game itself computes, so worlds and server permissions stay stable across launches.

Microsoft accounts sign in through the device code flow. Vesper shows you a short code and a URL, you approve it in a browser, and that is it. No embedded browser window, which is the part that usually breaks. Refresh tokens are encrypted at rest with DPAPI on Windows.

An honest note about offline skins

Skin rendering happens on each viewer's machine. Vesper can make your client render skins and capes for local accounts, including resolving other players' real skins by username on offline servers. What it cannot do is make a vanilla client render your custom skin, because that client never asked us.

So: your custom skin is visible to you and to anyone else running the Vesper mod. It is not visible to players on unmodified clients. No launcher can change that, and any that claims otherwise is not being straight with you.

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Install

Grab the latest build from Releases.

Platform	File	Notes
Windows	VesperLauncher-<version>-Setup.exe	Installer. Per-user, so no admin prompt
macOS (Apple Silicon)	...-osx-arm64.dmg	See the Gatekeeper note below
macOS (Intel)	...-osx-x64.dmg	See the Gatekeeper note below

The Windows installer puts Vesper in %LOCALAPPDATA%\Programs\VesperLauncher, adds Start menu and desktop shortcuts, and registers an entry in Add or remove programs. Because it installs per-user it never asks for administrator rights. Uninstalling offers to keep or delete your profiles, worlds and downloaded game files, and keeps them by default.

macOS builds are unsigned. Notarisation requires a paid Apple Developer account. Until that is in place, right-click the app and choose Open the first time, or run:

xattr -dr com.apple.quarantine "/Applications/Vesper Launcher.app"

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Build from source

You need the .NET 10 SDK. For the mod, you also need JDK 21.

git clone https://github.com/AroseEditor/Vesper-Launcher.git
cd vesper-launcher

dotnet restore
dotnet build
dotnet test

dotnet run --project src/Vesper.App

To produce a self-contained binary for your platform:

dotnet publish src/Vesper.App -c Release -r win-x64 \
  --self-contained true -p:PublishSingleFile=true -o publish

Swap win-x64 for osx-arm64 or osx-x64 as needed.

Linux is not built for releases. The code is cross-platform and CI still compiles and tests on Linux, so -r linux-x64 will work if you publish it yourself, but no Linux artifact ships.

Building the Windows installer

Needs NSIS on the path. Publish to a folder first, then run makensis:

dotnet publish src/Vesper.App -c Release -r win-x64 \
  --self-contained true -p:PublishSingleFile=false -o publish/win-x64

mkdir -p artifacts
cd installer

makensis /DAPP_VERSION=0.1.0 /DVI_VERSION=0.1.0.0 \
  /DSOURCE_DIR=..\publish\win-x64 \
  /DOUT_FILE=..\artifacts\VesperLauncher-0.1.0-Setup.exe \
  vesper.nsi

The installer must be built from a folder publish, not a single-file one.

Building the mod

The mod is a separate Gradle project under mod/. It needs JDK 21 (Gradle cannot run on Java 25) and Gradle 8.9. It builds for Fabric and NeoForge.

Forge is not supported on 1.21: Architectury's architectury-forge artifact stops at 11.1.17, which targets 1.20.x. NeoForge is Forge's successor for 1.21 and is what Vesper targets instead. No Gradle wrapper is committed, so either use a system Gradle:

cd mod
gradle build

or generate a wrapper once and use that afterwards:

cd mod
gradle wrapper
./gradlew build

The first build downloads and decompiles Minecraft through Architectury Loom, so expect it to take several minutes. This build is not yet verified - see the roadmap. CI attempts it on release but is configured not to block a launcher release if it fails.

Regenerating the icon

python brand/generate_icon.py

This draws the icon procedurally and writes icon.png, icon-wordmark.png, icon.ico, and every size under brand/generated/. To use your own artwork instead:

python brand/generate_icon.py --source path/to/your-art.png

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How it is put together

src/
  Vesper.Core/        Launcher logic with no UI. Paths, profiles, accounts, auth, loaders,
                      mods, servers, skins, themes, versions, launching
  Vesper.App/         Avalonia UI. Views, viewmodels, theme application, icons, 3D skin control
  Vesper.Core.Tests/  Unit tests
mod/                  Gradle multiloader project for the Vesper client mod
  common/             Shared logic: motion blur, HUD layout, config, skin resolution
  fabric/ neoforge/   Loader entrypoints
brand/                Icon source and generator
scripts/              Convention checks used by CI

The 3D skin viewer is a software rasteriser written from scratch in Vesper.Core/Skins. It has a z-buffer, per-face shading and a pick buffer, which is what lets you paint pixels directly onto the rotating model rather than only onto a flat texture.

The mod's motion blur is frame-accumulation, the same approach Lunar and Badlion use, not an Iris or OptiFine shaderpack. Its blend factor is frametime-normalised, so the effect has an identical half-life at 60, 120 and 240 frames per second.

The launcher is C# on .NET 10 with Avalonia 12 for the interface, and leans on CmlLib.Core for the genuinely hard parts of launching Minecraft: version manifest resolution, library rule evaluation, native extraction, asset indexing, and classpath construction.

Microsoft authentication is implemented directly against Microsoft's endpoints rather than through MSAL, which keeps it working identically on all three platforms and makes a custom client ID a one-line setting.

Where your files go

Vesper stores everything under %LOCALAPPDATA%\VesperLauncher on Windows, or the platform equivalent elsewhere. Drop a portable.txt next to the executable and it will use a VesperData folder beside itself instead.

vesper.json            Global settings
accounts.json          Accounts. Microsoft refresh tokens encrypted at rest
themes/                Your theme files
runtime/               Managed Java runtimes
shared/                Assets, libraries and version manifests, shared across instances
instances/<id>/
  instance.json        Version, loader, RAM, Java, mods
  .minecraft/          Isolated game directory. Saves, mods, config, resource packs
servers/<id>/          Paper or Purpur server, world, plugins

Shared libraries with isolated game directories is the model Prism uses, and it is why adding your twentieth instance costs almost no disk space.

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Theming

A theme is a JSON file of colour tokens. Every brush in every view binds to one of these, which is what makes "change all the colours" actually work rather than leaving stragglers behind.

Token	Default	Used for
bgBase	#0A0A0C	Window background
bgElevated	#121216	Title bar, sidebar
bgCard	#1A1A20	Cards, popovers
bgHover	#23232B	Hover states
borderSubtle	#26262F	Dividers, card edges
borderStrong	#3A3A47	Popover edges
accent	#B57EDC	Primary actions, active nav
accentHover	#C9A0DC	Accent hover
accentDeep	#9A5FC4	Avatars, depth
accentBreath	#D14FE8	Dragon breath highlight, glow
accentContrast	#12060F	Text on accent
textPrimary	#F2EEF6	Body text
textMuted	#A9A2B5	Secondary text
textFaint	#6E6880	Labels, metadata
success warning danger		Status colours

To make your own, copy a built-in theme, change what you like, and drop it in themes/:

{
  "name": "My Theme",
  "colors": {
    "bgBase": "#08080A",
    "accent": "#7EDCC4",
    "accentBreath": "#4FE8C8"
  }
}

Any token you leave out falls back to the Mauve Black default, so a three-line theme is perfectly valid.

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Roadmap

• Core launch pipeline with isolated profiles and shared assets
• Local and Microsoft accounts
• Theme system and animated application shell
• Cross-platform CI with drafted releases
• Loader installers for Fabric, Quilt, Forge, NeoForge and OptiFine import
• Version browser with per-profile loader and loader-version selection
• Mods manager with Modrinth and CurseForge browsing
• Skins page with a 3D model editor
• Servers tab with Paper install, live console and a full server.properties editor
• playit.gg tunnel management
• Vesper mod builds for Fabric and NeoForge with an in-game menu, 37 modules and a live HUD
• Motion blur render pass with Lunar and Badlion presets
• Remaining module behaviours (entity culling, particle limit, glint, fullbright)
• Vesper Loader one-click profiles

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Run the checker before pushing:

python scripts/check_conventions.py

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License

Source-available, not MIT. See LICENSE.

You may use, study, modify and redistribute Vesper, including commercially. What you may not do is strip the attribution, rebrand it, and pass it off as your own work. Forks must keep the licence and the credit to ayush.ue5 and Zayrix , must say clearly that they are modified, and must use their own name and logo rather than Vesper's.

Vesper Launcher is not affiliated with, endorsed by, or associated with Mojang Studios or Microsoft. Minecraft is a trademark of Mojang Studios. Vesper downloads game files from Mojang at runtime and redistributes nothing.