Florian ERNSTandCodex
ebc1d17ea3
Use the existing Identifier parser at preserved-component decode/encode boundaries. Own current Game/fresh Java focused gate94/103->103/103; unchanged full106 improves94/106->103/106 with exactly3 separate empty-elision reads retained. Core round-trip old-fail/fixed-pass,66item tests pass. Clippy, docs and content-root checks pass; existing Python release-fixture failures retained. Co-Authored-By: Codex <[email protected]>
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Horizon
Minecraft: Java Edition 26.3, rewritten in Rust. Same worlds, same rules, same terrain, checked against the Java game by more than 300 differential harnesses. Free, open source and unofficial.
Not an official Minecraft product, nor approved by or associated with Mojang or Microsoft. Horizon contains no Minecraft code, assets or data: you need your own copy of Java Edition 26.3.
Download
Get the Horizon launcher from playhorizon.dev or the launcher releases (Linux x86-64, macOS on Apple Silicon, macOS on Intel from the next Nightly, Windows x64). It installs and updates the game, prepares its files from your copy of Minecraft, and updates itself.
You need a Microsoft account that owns Java Edition (why) and a GPU with Vulkan or OpenGL 3.3 (Linux), Vulkan or DirectX 12 (Windows), or a Mac (Apple Silicon, or Intel from the next Nightly). An existing Minecraft install (official launcher, Prism, MultiMC...) is reused; without one, Play downloads 26.3 from Mojang for your account. Step by step: Install and first launch.
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What works today
- The game: vanilla world generation, mobs, villagers, raids, redstone, every command, the HUD and the recipe book, on vanilla saves. Worlds from 1.8 to 26.2 are upgraded. Status.
- Extras: new menus, graphics presets, distant terrain up to 1024 chunks, controllers, zoom, minimap and more, off by default where they change the vanilla look. Settings.
- Packs: resource packs, and data packs with functions, predicates, item modifiers and world generation.
- Multiplayer: invite friends with a code, Open to LAN, join servers (online mode included). Multiplayer.
- Mods: content mods (blocks, items, data) and native Rust mods, built by the launcher with nothing to install. Java mod jars do not run. Mods.
In the Rust client, with vanilla assets and no mods or shaders:
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Host a server
The launcher's Servers page creates, starts, backs up and updates a server, and invites friends over Tailscale. On a VPS, horizon-server installs with one command and needs no Java. Host a server (reference).
Modpacks
The launcher imports Modrinth and CurseForge packs and plays the mods Horizon can carry over: today, content mods made of data and assets, not Java code. Modpacks.
Agent control
AI agents and scripts can play Horizon. horizon-ctl, shipped with the game, reads its state as JSON and acts like a player; horizon-ctl mcp serves the same commands over MCP.
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 done and reply with the result; horizon-ctl help lists them all. Agent control.
Build from source
Needs Rust 1.90+, Python 3.10+, JDK 25, and on Linux libasound2-dev libudev-dev. horizon-prepare builds the game's resources from your own copy of Java Edition 26.3 (checked against research-lock.json) and never downloads it:
- Client: play 26.3 once in the official launcher. Horizon reads
~/.minecraft(or--minecraft-dir/HORIZON_MINECRAFT_DIR). - Server jar: the 26.3 server jar (
downloads.server.urlinversions/26.3/26.3.json), passed once with--server-jarorHORIZON_SERVER_JAR.
git clone https://github.com/horizon-rust/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
Prepared files land in the gitignored .local/: never commit or share them. Options, controls and architecture: the native client guide; all developer docs: docs/README.md.
Roadmap
What is in progress, what comes next and where to help: ROADMAP.md, or playhorizon.dev/hub with the work board and what shipped.
Contributing
Issues and pull requests are welcome: read CONTRIBUTING.md (vanilla first, small pull requests). Questions: Discord. Before a pull request, run the self-check and paste its output:
git config core.hooksPath .githooks
python3 tools/pr_ready.py
It runs rustfmt, clippy, the touched crates' tests, the Python tests, the public-tree check and the vanilla harnesses your change affects. Never commit game files, decompiled source or prepared resources.
Project status
Player-visible gaps: 0 open of the 833 the port ledger found, reading every vanilla 26.3 method against Horizon's code: vanilla behaviour a player would notice that Horizon doesn't have yet. By area: Animals 0; Monsters and bosses 0; Entities, projectiles, vehicles and decorations 0; Items, enchantments and inventories 0; Blocks, redstone and fluids 0; World, world generation and saves 0; Screens, HUD and client packets 0; Entity and block rendering, models 0; Server and players on the server 0; Mob AI, villagers and raids 0. This number goes down as gaps close (tools/parity_gaps.py); the harness results below say that what is tested matches.
The table is the project's own audit: every subsystem matches vanilla in every harness that compares it. 100% means 100% of what the harnesses compare, not that nothing else differs.
Java parity: 100%
Scores: 0 (absent), 0.25 (started), 0.5 (playable, major features missing), 0.75 (mostly complete) or 1 (complete and verified by differential tests); the percentage is their average. Last audited 2026-10-13: the harnesses pass on Linux and macOS. The port ledger adds a method-by-method view of what is ported.
| Subsystem | Score | Main gaps |
|---|---|---|
| Window, input and game loop | 1 | None: game loop, options, camera, auto-jump, toggle sprint/sneak and frame limiter match |
| Assets and resources | 1 | None: item models match over 196,290 stacks; the resource pack screen over 3,000 sessions |
| Network protocol and multiplayer | 1 | None: joins vanilla servers; the dedicated server matches vanilla's files, login, configuration, play and command tree; LAN discovery 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) and animations (296), HUD overlays (2,200 states), the recipe book (600), player list, subtitles and world border match |
| 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; worlds from 1.8 to 26.2 upgrade as vanilla's DataFixers do |
| Entities and physics | 1 | None: attributes, spawn rules, natural spawning (15,500 cases), raids and patrols (1,900), finalizeSpawn (24,000) and mob AI (92 scenarios) match |
| Interaction and inventory | 1 | None: menu clicks over 8,000 sequences; recipe book placement (6,000), buttons (1,200), saved book (1,500), loom and crafter screens (1,600) |
| Menus, HUD and chat | 1 | None: every command (758 over 39,685 inputs), scoreboards (81,000 operations), the player list (872,000 draw calls), chat and its suggestions (3,000 sessions) match |
| 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), container spills (4,000), copper golems and the sculk family (435 scenarios) match |
Known issues
Skins served over https show the default skin unless already cached; pack icons show the unknown-pack texture in game; item tooltips lack attribute lines.
Licence
MIT, for the project's original work; dependencies keep their own licences (notices). Minecraft is a trademark of Mojang Synergies AB; its code and assets belong to Mojang and Microsoft under the Minecraft EULA.
Author
Made by Ludovic Marie (@ludovic111).