Play Minecraft: Java Edition 26.3 in Rust — offline, no account, no launcher

Horizon is Minecraft: Java Edition rewritten from scratch in Rust: one fast native program, no Java, the same worlds and rules as the Java game. This fork removes all of the sign-in, so the game opens straight into a world as an offline player — no Microsoft account, no launcher, no login screen, and no internet check.

Free, and ready if Minecraft is already on this machine. Horizon is MIT-licensed and never checks whether you paid for anything. It plays using the game files you already have — from the official launcher or any third-party launcher (SKLauncher, TLauncher, Prism, MultiMC, ATLauncher, Modrinth App, HMCL…). Nothing is downloaded and nothing is signed in to.

You need: a Mac, Linux box or Windows PC, the game files from a launcher you already use, and the matching server jar (step 3). Everything else is free and open source. Not an official Minecraft product — see the licence.

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How to install it, step by step

Copy each block into a terminal, one step at a time. On macOS this takes about 10 minutes, most of it one automatic build. Windows and Linux work the same way.

Step 1 — Get the code

macOS and Linux:

git clone https://github.com/arman0824/horizon.git
cd horizon

Windows (PowerShell):

git clone https://github.com/arman0824/horizon.git
cd horizon

Step 2 — Install the two build tools

You need Rust (the language the game is written in) and JDK 25 (used once, to read your Minecraft files; no Java runs when you play).

Rust — macOS/Linux:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
. "$HOME/.cargo/env"
rustc --version        # 1.90 or newer

Windows: download and run rustup-init.exe, then reopen the terminal.

JDK 25 —

# macOS (Homebrew)
brew install openjdk@25
java -version          # "openjdk version \"25...\""

Linux: sudo apt install openjdk-25-jdk (or your distro's equivalent). Windows: install Temurin 25 or any JDK 25.

Step 3 — Get the server jar (one file, 62 MB)

Horizon builds the game's data from your client jar and the matching server jar. If your launcher already has one, skip ahead. Otherwise:

• Open ~/Library/Application Support/minecraft/versions/26.3/26.3.json (macOS) or %APPDATA%\.minecraft\versions\26.3\26.3.json (Windows), copy the URL after "server": { "url": " …
• …or just search minecraft server 26.3 download and use Mojang's own download page

Then check the file you downloaded, and put it somewhere permanent:

shasum -a 1 ~/Downloads/server.jar
# must print: 33680f5f2ac32864d6d7cf5e56a705fdb3e05f4c
mkdir -p ~/Games && mv ~/Downloads/server.jar ~/Games/server.jar

Step 4 — Build the game

~/.cargo/bin/cargo build --profile fast -p horizon-client -p horizon-prepare

About 5 minutes on Apple silicon; a binary lands in target/fast/.

Step 5 — Turn your Minecraft files into the game's resources

./target/fast/horizon-prepare --prepare --server-jar ~/Games/server.jar

It looks for your game files by itself — ~/.minecraft on Linux/Windows, ~/Library/Application Support/minecraft on macOS — or you name the folder:

./target/fast/horizon-prepare --prepare --minecraft-dir /path/to/.minecraft --server-jar ~/Games/server.jar

It copies nothing off your machine, downloads nothing, and asks for no account. It ends with Prepared Horizon native-client resources: … (about 20 seconds).

If step 5 fails with "is not a 26.3 version file Horizon knows"

That means your launcher (SKLauncher, TLauncher and friends) rewrites the version file, so its checksum no longer matches. Fix it once — your launcher's folder is not touched:

mkdir -p .local/minecraft/26.3
curl -o .local/minecraft/26.3/manifest.json \
  https://piston-meta.mojang.com/v1/packages/11f1aefe473eefba0af62e3286c33b692807b2eb/26.3.json
shasum -a 1 .local/minecraft/26.3/manifest.json    # 11f1aefe473eefba0af62e3286c33b692807b2eb
./target/fast/horizon-prepare --prepare --server-jar ~/Games/server.jar

Step 6 — Play

./tools/play-offline.sh

The window opens in seconds. No account, no sign-in, nothing to click through. Your worlds, settings and player name live in ~/horizon-game/, so they survive every rebuild.

Press Esc any time to open the menu; single player, LAN and offline-mode servers all work from there.

Nice to know:

./tools/play-offline.sh --creative                 # creative mode
./tools/play-offline.sh --seed 1234                # a world of your own seed
./tools/play-offline.sh --world "New World"        # open a world you already had
./tools/play-offline.sh --name Steve               # your own player name
./target/fast/horizon-client --help                # every option

Optional: sound

The game starts silent. To copy vanilla sounds (~380 MB) from your install, once:

./target/fast/horizon-prepare sounds

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What this fork changed, and what it costs

One commit (6b82ad3) removes the sign-in surface and nothing else:

• --session-file, --session-stdin, HORIZON_SESSION_FILE — how a signed-in account was handed to the game. They are now refused as unknown options.
• HORIZON_ACCOUNT_SESSIONS — how splitscreen players signed in.
• The Microsoft sign-in and the launcher are not part of the build at all.

The engine itself — world generation, physics, rendering, netcode, saving — is untouched, so all of vanilla's differential tests still mean what they meant upstream.

This buys you: single player, LAN worlds, offline-mode servers, content mods, resource and shader packs, the horizon-ctl scripting interface, and a startup with no account round-trip at all.

It costs you: servers in online mode will refuse you (they require a real Microsoft session), skins don't load from Mojang, and Play with Friends is out. None of that touches how the game plays.

Full details: docs/forking.md · upstream project: horizon-rust/horizon

Troubleshooting

What you see	What to do
is not a 26.3 version file Horizon knows	Step 5's fix, above
No 26.3 server jar	Give it --server-jar PATH (step 3)
prepared game files are missing	Run step 5, or pass --resources .local/horizon-client/26.3
--session-file: unknown option	Expected — this fork signs nobody in
A server refuses you with invalidSession	It is in online mode; this fork cannot join it
The game is quiet	horizon-prepare sounds
Items missing in an old modded world	The mod's files weren't present at step 5

Licence and credit

Horizon is MIT-licensed, © Ludovic Marie and its contributors; this fork keeps that licence and attribution. Horizon contains no Mojang code and no Mojang assets: it reads the game files you already have, prepares them on your own machine into .local/, and never copies them anywhere else. You must have the game files from a launcher you already use.

NOT AN OFFICIAL MINECRAFT PRODUCT. NOT APPROVED BY OR ASSOCIATED WITH MOJANG OR MICROSOFT. Minecraft is a trademark of Mojang Synergies AB; its code and assets belong to Mojang and Microsoft under the Minecraft EULA.