[opensourcedex]

horizon is a free, open source gaming project written in Rust and released under MIT. It has 2,537 GitHub stars, 173 forks and 438 open issues, and was last pushed 13 hours ago. On this registry it ranks #49 of 69 tracked projects in Gaming, with 5 head-to-head comparisons available.

What is horizon?

Horizon is an unofficial, MIT-licensed reimplementation of Minecraft: Java Edition 26.3 written from scratch in Rust, made for players who already own a legal copy of the Java game and want to run their existing worlds through a native client installed by the Horizon launcher.

What it is

Horizon is a native game that lives in the Minecraft: Java Edition ecosystem: it reads the same worlds, follows the same rules and generates the same terrain as the Java game, and it is checked against that game by 281 differential harnesses. It contains no Minecraft code, assets or data, so the launcher prepares its files from the user's own legally obtained copy of Minecraft: Java Edition 26.3. It is free, open source and explicitly not an official Minecraft product, nor approved by or associated with Mojang or Microsoft.

The concrete problem it solves is the Java client itself. Horizon replaces the game process that normally runs on the JVM with a Rust binary rendering through Vulkan and wgpu, while keeping saves in vanilla's format and upgrading worlds from 1.8 to 26.2 exactly as vanilla does. A Java 25 runtime is needed only for the one-time preparation of game files, and horizon-server runs without Java at all.

Key capabilities

  • Behaviour is verified against vanilla by 281 differential harnesses, which is the project's stated basis for claiming the same rules and terrain.
  • Singleplayer reproduces vanilla world generation, mobs, villagers, raids, redstone, every command, the HUD and the recipe book, on saves in vanilla's format.
  • Rendering runs on Vulkan via wgpu, with distant terrain up to 1024 chunks, graphics presets, controller support, optional zoom and a minimap — all off by default where they would change the vanilla look.
  • Resource packs work, and data packs load functions, predicates and item modifiers.
  • Mods use Horizon's own system of Rust compiled to WebAssembly; Java mod jars do not run.
  • Multiplayer covers inviting friends from the pause menu's Friends button with a code, Open to LAN, and joining offline-mode servers.
  • horizon-ctl, shipped beside the game in every release folder, reads the game as JSON and acts like a player, and horizon-ctl mcp serves the same commands as an MCP server with screenshots returned as images.

Who uses it and how

  • Singleplayer players carrying forward existing saves, including worlds created between versions 1.8 and 26.2, which are upgraded the way vanilla upgrades them.
  • Small groups playing cooperatively without a dedicated server, using the pause-menu Friends code or Open to LAN.
  • Self-hosters running a VPS: the launcher's Servers page creates, starts, backs up and updates a Horizon server with buttons and invites friends over Tailscale, while horizon-server installs with one command.
  • Modpack players importing a Modrinth or CurseForge pack through the launcher's Modpacks page, which shows which mods Horizon can carry over and plays those as their own profile.
  • Automation and research setups where agents or scripts drive the game, for example horizon-ctl launch --world Survival --seed 5 --wait followed by horizon-ctl find-block birch_log and horizon-ctl goto.

Getting started

Install through the Horizon launcher, available from playhorizon.dev or the launcher releases page for Linux x86-64, macOS on Apple Silicon and Windows x64; the launcher installs and updates the game and prepares its files from your own copy. You need Minecraft: Java Edition 26.3 played once, a Java 25 runtime for that preparation, and a GPU with Vulkan on Linux and Windows or any Apple Silicon Mac.

How it compares

No comparable reimplementation is named in the facts, so Horizon stands alone in this registry rather than sitting in a field of rivals. The other tools the README mentions — the official launcher, Prism and MultiMC — are not alternatives to it; they are simply ways of playing Minecraft once so that Horizon's launcher can prepare files from that copy.

When to use it — and when not to

A self-hoster must supply a legally obtained copy of Minecraft: Java Edition 26.3, a Java 25 runtime for the one-time preparation, and a Vulkan-capable GPU or Apple Silicon machine, and anyone hosting remotely also operates horizon-server themselves. It is not the right choice for players who need Microsoft account sign-in, since Horizon cannot sign in yet and therefore cannot join servers that check accounts, nor for anyone dependent on Java mod jars, which do not run; modpacks are limited to content mods made of data and assets. The project also carries 438 open issues, so it should be treated as actively moving rather than settled.

project readme (upstream, from github) — read inline

CI Minecraft Java 26.3 Rust Vanilla parity 100% Linux, macOS and Windows MIT license

Website · Download · Documentation · Release notes · Roadmap · Project status · Contributing

Horizon

Horizon is Minecraft: Java Edition 26.3 rewritten in Rust: a native game that reads the same worlds, follows the same rules and generates the same terrain as the Java game, and is checked against it by 281 differential harnesses. You play it through a small launcher, on the files from your own copy of Minecraft. It is free, open source and unofficial.

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

Horizon is installed through the Horizon launcher. Get it from playhorizon.dev (the Download button picks your system) or from the launcher releases, for Linux x86-64, macOS on Apple Silicon or Windows x64. The launcher installs and updates the game, prepares its files from your own copy of Minecraft, and updates itself.

You need Minecraft: Java Edition 26.3, played once (the official launcher, Prism, MultiMC and other launchers all work); a Java 25 runtime, for the one-time preparation; and a GPU with Vulkan on Linux and Windows, or any Apple Silicon Mac. Step by step, with macOS's first-open prompt and the first launch: Install and first launch.

What works today

The documentation covers each of these.

  • The game: singleplayer with vanilla's world generation, mobs, villagers, raids, redstone, every command, the HUD and the recipe book, on saves in vanilla's format. Worlds from 1.8 to 26.2 are upgraded as vanilla does. Status table.
  • Horizon's own extras: new menus (vanilla's are one setting away), graphics presets, distant terrain up to 1024 chunks, controller support, optional zoom, minimap and more, all off by default where they would change the vanilla look. See Settings.
  • Resource packs and data packs: resource packs work, and data packs load functions, predicates and item modifiers.
  • Playing with others: invite friends from the pause menu's Friends button with a code, Open to LAN, and joining offline-mode servers. Horizon cannot sign in to a Microsoft account yet, so it cannot join servers that check accounts. See Multiplayer.
  • Mods: Horizon has its own mod system (Rust compiled to WebAssembly). Java mod jars do not run. See Mods and data packs.

Screenshots, captured in the Rust client itself with vanilla assets and no mods or shaders:

Host a server

The launcher's Servers page creates, starts, backs up and updates a Horizon server with buttons, and invites friends over Tailscale. On a VPS, horizon-server installs with one command and runs without Java. Guide: Host a server (reference).

Modpacks

The launcher's Modpacks page imports a Modrinth or CurseForge pack, shows which of its mods Horizon can carry over, and plays the ones it can as their own profile. Today that means content mods made of data and assets; mods with Java code are not ported yet. See Modpacks.

Agent control

AI agents and scripts can play Horizon. horizon-ctl, shipped beside the game in every release folder, is a command line that reads the game as JSON and acts like a player; horizon-ctl mcp serves the same commands as an MCP server (one tool per command, screenshots returned as images).

horizon-ctl launch --world Survival --seed 5 --wait   # finds the version the launcher installed
horizon-ctl state                                       # position, health, food, target, screen...
horizon-ctl find-block birch_log                        # the nearest logs
horizon-ctl goto -0.5 65 -2.5 --near 2.5                # walks there along a path
horizon-ctl break -1 65 -3                              # mines it; replies with the drops
horizon-ctl open-inventory && horizon-ctl click-slot 0  # menus: slots, buttons by label, text fields

Commands block until the action is done and reply with what happened; errors are JSON with distinct exit codes, horizon-ctl help lists every command and horizon-ctl COMMAND --help explains one with examples. It talks to the game over a Unix socket on Linux and macOS and over a token-protected localhost port on Windows. See Agent control in the native client guide.

Build from source

For developers. Requirements: Rust 1.90 or newer, Python 3.10 or newer, JDK 25, and on Linux the ALSA and udev development headers (libasound2-dev libudev-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
cargo run --release -p horizon-prepare -- --prepare --server-jar ~/Downloads/server.jar   # needs JDK 25
cargo run --release -p horizon-prepare -- sounds   # 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 developer documentation is indexed in docs/README.md, including the parity workflow.

Roadmap

What is being done now, what comes next and where you can help, in plain words and in technical detail: ROADMAP.md. playhorizon.dev/hub shows it with the work board, the journal of what shipped and how to help.

Contributing

Issues and pull requests are welcome: see CONTRIBUTING.md for how we work (vanilla first, small pull requests, labels), or the contributing guide on the site. Questions and ideas: Discord. Before opening a pull request, run the self-check and paste the block it prints:

git config core.hooksPath .githooks
python3 tools/pr_ready.py

It runs rustfmt, clippy with warnings denied, the tests of the crates you touched, the Python tests, the public-tree check, and the vanilla harnesses your change can affect. CI runs the same checks on GitHub's Linux runners; the vanilla harnesses need the game, which Horizon never downloads, so they run on a maintainer's computer holding their 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.

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 are listed below.

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

Known issues

Horizon can't sign in to a Microsoft account yet, so it can't join online-mode servers (it joins offline-mode ones); 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.

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.

Third-party credits and licenses: Third-party notices.

Author

Made by Ludovic Marie (@ludovic111).

Frequently asked questions

Is horizon free to use?

horizon is open source under the MIT licence. There is no licence fee and no seat count — you can self-host it or, where the project offers one, pay a vendor for a managed version instead.

What does horizon do?

Minecraft: Java Edition 26.3 rewritten from scratch in Rust, checked against vanilla with 281 differential harnesses. Get it with the Horizon launcher.

What is horizon written in?

horizon is primarily written in Rust. Its source is publicly available at https://github.com/ludovic111/horizon, and it has 2,537 GitHub stars.