Horizon APIs · Horizon docs

Horizon has six surfaces that other programs and people build on. Each one has an API (the contract: what you may call, read or write, and what Horizon promises about it) and an SDK (the tools that help you use it). This section has one page per surface, plus the rules every surface follows: stability and versioning.

Surface	For	API today	Stability	Reference
Mods	mod authors	WIT `horizon:mods@0.1.0`, manifest `api` 0.1 (code) and 0.2 (content)	preview	mods-reference.md (generated)
Shaders	shader authors	none yet: packs were removed on 2026-10-24	planned	none
Agent control	agents, scripts, tests	`horizon-ctl`, its MCP server, the game's control socket	preview	horizon-ctl-commands.md (generated)
Servers	hosts, panels, bots	`horizon-server` commands, `server.toml`, control API `/api/v1`	stable	server-reference.md (generated)
Launcher	players' agents, pack makers	`horizon-launcher` commands and its MCP server	preview	launcher-commands.md (generated)
Data formats	tools that read Horizon's files	benchmark reports, telemetry, settings files, signed checksums	stable or preview, per format	on that page

How these APIs are designed

From the people who use them. Each API starts from what a mod author, a pack author, a server host or an agent needs to do, written down as tasks ("a host backs up the world from a script"), and from how Horizon is built: Rust, wgpu, WebAssembly components and a server thread that runs every world. A function exists because a task needs it.
Our own design. Horizon's APIs are not modelled on any other project's. Contributors may know other mod loaders, renderers and server platforms exist, but their source and API references are never read, copied or paraphrased here, and our names, shapes and docs are not taken from theirs. Vanilla Minecraft 26.3 is the reference for game concepts: ids, commands, server.properties, data packs and resource packs.
Safe by default. Mods run in a sandbox and can only use the capabilities their manifest declares; the control sockets listen on this computer only, behind a token; nothing here is on by default where it would change vanilla's look or behaviour.
Free when unused. An API nobody uses costs nothing per tick or per frame: no engine, no thread, no allocation.
One contract for every mode. In-frame single player, the server thread, LAN and the dedicated server run the same gameplay code (AGENTS.md), so a server-side API serves all of them.

References are generated

A reference page is written by code from the source it describes, and a test fails when the two differ:

Page	Generated from	Update it with
mods-reference.md	`crates/horizon-mod-sdk/wit/horizon.wit`, the manifest's capabilities	`HORIZON_WRITE_DOCS=1 cargo test -p horizon-mods --features pack --test api_reference`
server-reference.md	`horizon-server`'s help, `config::TEMPLATE`, `api::ROUTES`	`HORIZON_WRITE_DOCS=1 cargo test -p horizon-server reference`
horizon-ctl-commands.md	the command table in `crates/horizon-client/src/bin/horizon-ctl/commands.rs`	`horizon-ctl help --markdown > docs/horizon-ctl-commands.md`
launcher-commands.md	`launcher/src/cli.rs`	`HORIZON_WRITE_DOCS=1 cargo test --manifest-path launcher/Cargo.toml the_launcher_reference`

So a pull request that changes an API also changes its reference, and the reviewer sees the API's diff in the reference's diff. The guides (overview, how-to, examples) are written by hand.

Each surface's page

Every page has the same parts: Overview (what you can build), Guide (where to start), Reference, Examples, Stability (the level of each part, per stability.md), Changelog and Not there yet (what is planned, so nobody builds on a guess).

The website shows these pages at playhorizon.dev/docs/api, built from this folder, and a summary for players and authors at playhorizon.dev/docs/apis (website/docs/apis.md).

Not an official Minecraft product. Not approved by or associated with Mojang or Microsoft.