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Horizon

A Rust rewrite of Minecraft: Java Edition 26.3 built for one-to-one vanilla parity, checked against the game itself with differential tests.

Every subsystem matches vanilla in all 281 parity harnesses, on Linux and macOS: 100% of what the harnesses compare (see Project status). The native client is playable on Linux, macOS (Apple Silicon) and Windows.

Not an official Minecraft product. Not approved by or associated with Mojang or Microsoft. Horizon contains no Minecraft code, assets or data: you need your own legally obtained copy of Minecraft: Java Edition 26.3.

Download

Download the Horizon launcher (or see playhorizon.dev) for Linux x86-64, macOS Apple Silicon or Windows x64: take the newest launcher-v* release (currently launcher-v0.1.1); the launcher then updates itself. The launcher is the way to get Horizon: it installs and updates the game, prepares its resources from your own copy of Minecraft, and starts the client or a dedicated server.

You need Minecraft: Java Edition installed with the official launcher, with 26.3 played once; Python 3.10 or newer and Java 25 (a JDK, e.g. Eclipse Temurin 25) for the one-time resource preparation; and a GPU with Vulkan on Linux and Windows, or any Apple Silicon Mac.

The launcher

It lists Horizon's releases and installs the build for your platform, shows each release's patch notes and the roadmap, updates Horizon and itself, and doubles as a command-line tool and an MCP server. See the launcher's README.

Screenshots

Captured in the Rust client itself, with vanilla assets and no mods or shaders.

	Vanilla world generation ported to Rust (terrain, aquifers, carvers, features, villages and the Nether), every block model with smooth lighting and biome tints, the vanilla sky and fog, mobs, the HUD, chat and advancements: everything in these frames is drawn by Horizon.

What it does

Horizon reimplements the Minecraft Java client and its game logic in Rust, one subsystem at a time, and compares each piece with the vanilla game. Each tools/test_*_parity.py harness drives the same inputs through Horizon and through the vanilla client and server bytecode from your own copy of the game, then checks that the outputs are identical. It is for players and developers interested in game reimplementation, and for anyone who wants to see how far a behaviour-exact native rewrite can go.

The native client opens on a vanilla-style title screen with world creation and selection, and generates worlds with the Rust port of the vanilla generators: noise terrain, aquifers, surface rules, carvers and placed features, all checked against vanilla. It streams and lights chunks on worker threads and renders every vanilla block model with smooth lighting, biome tints, the vanilla sky, sun, moon, stars and clouds. Gameplay includes:

• validated player physics, health and hunger;
• mining with vanilla tool rules and loot tables;
• placing, crafting, chests and furnaces;
• dropped items, particles and sounds;
• passive and hostile mobs with combat and vanilla AI, including guardians, shulkers, illagers, ravagers, the wither, the ender dragon fight, the breeze, the creaking, the sniffer, the happy ghast, llamas and the copper golem;
• villagers that take jobs, trade, restock, meet at the bell and sleep in beds, on a port of vanilla's brain;
• raids and pillager patrols;
• dispensers, crafters, the loom and the recipe book;
• every command, scoreboards and teams, the player list, subtitles and the HUD overlays;
• boats, minecarts, item frames, paintings and armor stands;
• shields, maps, books, fireworks, beacons, advancements and statistics;
• Anvil saves, joining vanilla servers, and opening a world to LAN.

Build from source

For developers. Requirements: Rust 1.90 or newer, Python 3.10 or newer, JDK 25, and on Linux the ALSA development headers (libasound2-dev on Debian and Ubuntu). Development and the vanilla harnesses run on Linux.

Horizon contains no game files and never downloads them. It builds its resources from your own copy of Minecraft: Java Edition 26.3, verified against the checksums in research-lock.json:

1. Client: install Java Edition with the official launcher and play 26.3 once. Horizon reads versions/26.3/, libraries/ and assets/ from the launcher's game directory (~/.minecraft on Linux). If yours lives elsewhere, pass --minecraft-dir or set HORIZON_MINECRAFT_DIR.
2. Server jar: the 26.3 server jar, from the downloads.server.url in your launcher's versions/26.3/26.3.json (or minecraft.net/download/server while 26.3 is the current release). Pass it with --server-jar or set HORIZON_SERVER_JAR. It is only needed the first time.

git clone https://github.com/ludovic111/horizon.git
cd horizon
python3 tools/prepare_native_client.py --prepare --server-jar ~/Downloads/server.jar   # needs JDK 25
python3 tools/fetch_sounds.py                      # optional: sounds from your launcher install
cargo run --release -p horizon-client

Everything prepared lands in the gitignored .local/. It is derived from the game: never commit it or share it.

The client starts on the title screen. Command-line options (--world, --seed, --creative, --render-distance, --dedicated), controls, scripting through horizon-ctl, and the architecture are described in the native client guide. The rest of the documentation is indexed in docs/README.md, including the parity workflow.

Project status

The table below is the project's own audit of each subsystem. Every subsystem now matches vanilla in every harness that compares it. 100% means 100% of what the harnesses compare, not proof that nothing else differs. The remaining known differences and the final checks are listed in the roadmap.

Java parity: 100%

Each subsystem scores 0 (absent), 0.25 (started, not playable), 0.5 (playable, major vanilla features missing), 0.75 (playable, mostly complete) or 1 (complete and verified against vanilla by differential tests). The percentage is the average; tests/test_parity.py keeps it in sync with this table. Last audited 2026-10-13 against the harness results: all 281 harnesses pass on Linux, each rerun whenever one of its inputs changed, and the Mac mini now runs every one of them too (Rust uses Java's own float maths on each platform).

Subsystem	Score	Main gaps
Window, input and game loop	1	None: the game loop, options, camera, auto-jump, toggle sprint/sneak, local input and the frame limiter match vanilla
Assets and resources	1	None: item models match vanilla over 196,290 stacks and the client draws every item through them; the resource pack screen matches vanilla's drawing over 3,000 sessions of clicks, scrolling and searching, its incompatibility confirmation included
Network protocol and multiplayer	1	None: joins vanilla servers; the dedicated server (--dedicated) matches vanilla's files, status ping, login, configuration, play, chunks, chat, recipes, advancements and command tree, a client built from vanilla's packet code joins it, Horizon joins a vanilla server, and LAN discovery matches over 462 cases (offline mode only)
Chunk storage and palettes	1	None: client and saves share paletted containers, identical to vanilla over 266 scenarios
Section meshing	1	None: 112 scenes and over a million quads identical to vanilla
Rendering	1	None: entity models, block entity renderers (407 cases, End portals, gateways and the loom's banner preview included) and their animations (296 cases, End gateway beams included), the HUD overlays (2,200 states), the recipe book (600 states), the player list, subtitles and the world border match vanilla
Lighting	1	None: saved and relit light matches vanilla, slabs and stairs included
World generation	1	None: 2,352 whole chunks over 225 structure sites, in all three dimensions, identical to vanilla
Region files and saves	1	None: saves round-trip with vanilla, and worlds from 1.8 to 26.2 upgrade as vanilla's DataFixers do, superflat worlds included; old options.txt and hotbar.nbt files are upgraded too
Entities and physics	1	None: attributes, dimensions, death loot, spawn rules, natural spawning (15,500 cases), raids and patrols (1,900 cases), spawned mobs' gear, enchantments and state (finalizeSpawn, 24,000 cases) and mob AI (92 scenarios: villager breeding and gossip, the warden, ghastlings and copper golems included) match vanilla
Interaction and inventory	1	None: menu clicks match over 8,000 click sequences, the loom and the crafter included; recipe book placement (6,000 cases), its buttons (1,200), the saved book (1,500) and the loom and crafter screens (1,600) match vanilla
Menus, HUD and chat	1	None: every command runs as vanilla (758 commands over 39,685 parsed inputs), scoreboards and teams match (81,000 operations), the player list matches over 872,000 draw calls with heads drawn from players' skins (authlib's textures, SkinManager's lookup, legacy skin conversion), and the chat matches focused and scrolled; the resource pack screen (selection over 4,000 cases, drawing and its incompatibility confirmation over 3,000 sessions) and the chat input with its command suggestions, usage lines, Tab completion and history (3,000 sessions on vanilla's client command tree) match vanilla
Audio	1	None: the sound engine, sound events, music, situational music, ambience and subtitles match vanilla
Block behaviours and ticking	1	None: block updates, random ticks, redstone, dispensers (6,000 cases), crafters (4,000 crafts), block entity removal (containers spill, 4,000 cases), copper golem chest sorting and the sculk family (435 scenarios: shrieker warnings and warden summoning included) match vanilla

Roadmap

Known differences. Online-mode servers (Mojang's session servers) are not supported; skins served over https show the default skin unless already cached; pack icons show the unknown-pack texture in game; the creative hotbar keys (C/X) aren't wired to the hotbar loader; item tooltips lack attribute lines.

Final checks. A from-scratch audit (tools/parity.py --all) on Linux and on macOS, and the launch checks on the packaged Linux, macOS and Windows builds listed in Rust rewrite status.

Next. With vanilla parity as the base:

• Performance: optimize the client and the server as far as they can go (rendering, chunk generation and meshing, memory, multithreaded ticking) while the differential harnesses keep gameplay identical to vanilla.
• Modding support: a stable API for writing mods against Horizon.
• Agent control: an MCP server and a CLI so AI agents and scripts can play and drive the game, growing out of today's horizon-ctl scripting socket.
• Built-in recording: capture gameplay video in a keypress, without external tools.
• Automatic version updates: a pipeline that ports each new Minecraft release on its own: compare the new version with the pinned one, regenerate the data, rewrite the changed parts and prove them with the same differential harnesses.

Contributing

Issues and pull requests are welcome. Before opening a pull request, run the offline checks:

git config core.hooksPath .githooks
python3 -m unittest discover -s tests -v
cargo fmt --all -- --check
cargo clippy --workspace --all-targets -- -D warnings
cargo test --workspace
python3 tools/check_public_tree.py --history

CI runs these checks on GitHub's Linux runners. The vanilla comparisons need the game, which Horizon never downloads, so they run only when started by hand on a self-hosted runner holding the maintainer's own copy. Never commit game files, decompiled source or prepared resources: tools/check_public_tree.py rejects them, and tracked Java is allowed only under the project's own dev/horizonlab namespace.

Licence

MIT, for the project's original work only. Dependencies keep their own licences. Minecraft is a trademark of Mojang Synergies AB; Minecraft code and assets belong to Mojang and Microsoft and are covered by the Minecraft EULA. Decompiled game source and prepared resources stay on your machine and are never published.

Author

Made by Ludovic Marie (@ludovic111).