mcpfabric

<div align="center"> <img src="docs/assets/mcpfabric-icon-512.png" alt="MCP Fabric grass block, AI network, and bridge emblem" width="180" height="180"> # MCP Fabric — AI control for Minecraft **Let Claude and other MCP clients see, understand, and play Minecraft through 50+ tools.** [](https://github.com/denfry/mcpfabric/actions/workflows/build.yml) [](https://modrinth.com/mod/mcpfabric) [](https://github.com/denfry/mcpfabric/stargazers) [](LICENSE) [](https://discord.gg/mVZcNUAGZt) [Download on Modrinth](https://modrinth.com/mod/mcpfabric) · [Installation](#quick-start) · [Tools](#tools-50) · [Security](SECURITY.md) · [Telemetry](docs/TELEMETRY.md) · [Contributing](CONTRIBUTING.md) </div> MCP Fabric is a local-first Minecraft mod and Model Context Protocol server that gives AI agents structured observation and controlled access to Minecraft. It works on both the client and dedicated servers across Minecraft 1.21.1–1.21.11 and 26.1–26.3, on Fabric and NeoForge. - **Play through natural language:** move, look, navigate, mine, build, fight, and use inventory. - **See the game:** inspect blocks, entities, players, status, chat, events, and screenshots. - **Operate servers:** run commands, edit worlds, manage entities, and administer players. - **Bring your own AI:** works with Claude Desktop, Claude Code, and other MCP-compatible hosts. - **Stay local by default:** loopback-only HTTP bridge, bearer authentication, and capability gates. - **No hidden telemetry:** the current Fabric release sends no usage analytics. ## Quick start 1. Install [Fabric Loader](https://fabricmc.net/use/installer/) and [Fabric API](https://modrinth.com/mod/fabric-api), or [NeoForge](https://neoforged.net/). 2. Download the jar matching your Minecraft version and loader from [Modrinth](https://modrinth.com/mod/mcpfabric/versions) and place it in `mods/`. 3. Launch Minecraft once, then copy `token` from `config/mcpfabric.config.json`. 4. Build the MCP server with `cd mcp-server && npm ci && npm run build`. 5. Add it to your MCP client using the [ready-to-copy examples](#3-connect-to-claude). > [!CAUTION] > MCP Fabric can grant an AI operator-level control. Keep the bridge on `127.0.0.1`, keep > authentication enabled, and disable capability groups you do not need. ## How it works `mcpfabric` has two parts: a Fabric / NeoForge mod that embeds a local HTTP bridge in Minecraft, and a small TypeScript MCP server that exposes the bridge as discoverable tools. ``` Claude / any MCP client │ MCP (stdio or streamable HTTP) mcp-server (Node / TypeScript) │ HTTP POST /rpc (JSON-RPC) + GET /events (SSE), bearer token, 127.0.0.1 only mod "mcpfabric" on Fabric or NeoForge (HTTP server embedded in Minecraft) │ all game access goes through the main-thread executor (server.execute / Minecraft.execute) ┌── common (env *) ─────────────┐ ┌── client (env client) ─────────────────┐ │ info world entities │ │ player control interact │ │ players command chat events │ │ inventory vision navigation chat │ └───────────────────────────────┘ └─────────────────────────────────────────┘ ``` Reads use Minecraft's native API (structured data); writes (`setblock` / `summon` / `give` / `tp` / effects / weather / time) go through the command dispatcher with output capture. Player control uses `KeyMapping` (integrating with the vanilla input pipeline), screenshots use the vanilla `Screenshot` / `NativeImage`, and navigation is a custom A\*. --- ## Supported Minecraft versions A single source tree targets many Minecraft versions using [Stonecutter](https://stonecutter.kikugie.dev/). Each version below ships its own jar: | Line | Versions (one jar each) | Java | |----------|-----------------------------------------------------------------|------| | 1.21.x | 1.21.1, 1.21.2, 1.21.3, 1.21.4, 1.21.5, 1.21.6, 1.21.7, 1.21.8, 1.21.9, 1.21.10, 1.21.11 | 21 | | 26.x | 26.1.2 (installs on 26.1–26.1.2), 26.2, 26.3 | 25 | 14 Fabric jars are produced, each named `mcpfabric-<modVersion>+<mcVersion>.jar` (e.g. `mcpfabric-0.3.0+1.21.8.jar`). The 26.1.2 jar declares compatibility with the whole 26.1 line. They require **Fabric Loader ≥ 0.19.5** and the matching **Fabric API** build. 13 NeoForge jars cover the same versions except 1.21.2 (NeoForge only shipped two abandoned betas for it), each named `mcpfabric-neoforge-<modVersion>+<mcVersion>.jar`: | Minecraft | Minimum NeoForge | |-----------|------------------| | 1.21.1 | 21.1.251 | | 1.21.3 | 21.3.97 | | 1.21.4 | 21.4.157 | | 1.21.5 | 21.5.98 | | 1.21.6 | 21.6.20-beta | | 1.21.7 | 21.7.25-beta | | 1.21.8 | 21.8.54 | | 1.21.9 | 21.9.16-beta | | 1.21.10 | 21.10.64 | | 1.21.11 | 21.11.45 | | 26.1.2 | 26.1.2.109 | | 26.2 | 26.2.0.88 | | 26.3 | 26.3.0.10-beta | NeoForge for 1.21.6, 1.21.7, 1.21.9 and 26.3 only exists as beta builds. The MCP server needs **Node.js ≥ 22.16** (the agent runtime uses the built-in `node:sqlite`). --- ## 1. Build the mod ```bash # Build a single version (the one currently active in stonecutter.gradle) ./gradlew build # Windows: gradlew.bat build # Build a specific version (Fabric nodes are named after the version, NeoForge nodes <mc>-neoforge) ./gradlew ":1.21.8:build" ./gradlew ":1.21.1-neoforge:build" # Build every supported version at once ./gradlew chiseledBuild ``` Per-version jars land in `versions/<node>/build/libs/`. > **JDK note.** 1.21.x builds need **JDK 21**; the 26.x line needs **JDK 25**. Loom requires the > Gradle daemon to run on a JDK at least as new as the Minecraft version, so to build 26.x (or > `chiseledBuild`) run Gradle on JDK 25 with JDK 21 also installed. See > [CONTRIBUTING.md](CONTRIBUTING.md#jdk-requirements). > **Network note.** If the first build fails with `Remote host terminated the handshake` while > downloading dependencies from `maven.fabricmc.net` (this happens behind TLS-inspecting > antivirus/firewalls), `gradle.properties` already pins TLS 1.2 and sequential downloads. Just > re-run the build — the download cache persists. ### Install Drop the jar for your Minecraft version and loader into your `mods/` folder (on Fabric, together with **Fabric API**): - **Client** (AI plays as you): the `mods/` folder of your Fabric / NeoForge instance. - **Server** (AI as admin): the `mods/` folder of your dedicated Fabric / NeoForge server. - Both sides at once is fine. On first launch the mod creates `config/mcpfabric.config.json` and logs where to find the token: ``` [mcpfabric] ready — bridge http://127.0.0.1:25599 (token: .../config/mcpfabric.config.json) ``` Copy the `token` value from that file — the MCP server needs it. The token is intentionally not printed to logs. ### Mod config (`config/mcpfabric.config.json`) ```json { "host": "127.0.0.1", "port": 25599, "token": "generated automatically", "requireAuth": true, "callTimeoutMs": 8000, "worldIdKey": "generated automatically", "enableWorldWrite": true, "enableCommands": true, "enablePlayerControl": true, "enableVision": true } ``` The `enable*` flags let you switch off dangerous capability groups. `requireAuth` (default `true`) gates every request behind the bearer token — only set it to `false` if you understand that it removes the sole authentication on an operator-level bridge. Keep `host` on `127.0.0.1` unless you fully understand the consequences — the bridge grants operator-level power. `worldIdKey` turns a server address into the opaque world id that `session.info` reports; like the token, it is never sent over the bridge. --- ## 2. MCP server ```bash cd mcp-server npm install npm run build # compiles to dist/ ``` Usually your MCP client launches it for you (see below). Manually: ```bash MCPFABRIC_URL=http://127.0.0.1:25599 MCPFABRIC_TOKEN=<token> node dist/index.js ``` ### Environment variables | Variable | Default | Description | |------------------------|--------------------------|---------------------------------------------------| | `MCPFABRIC_URL` | `http://127.0.0.1:25599` | Address of the mod's HTTP bridge. | | `MCPFABRIC_TOKEN` | — | Bearer token from the mod config (required by default). | | `MCPFABRIC_TIMEOUT_MS` | `15000` | Per-call timeout to the bridge. | | `MCPFABRIC_TRANSPORT` | `stdio` | `stdio` or `http`. | | `MCPFABRIC_HTTP_PORT` | `25600` | Port for the `http` transport (`/mcp`). | --- ## 3. Connect to Claude ### Claude Desktop `claude_desktop_config.json` (see `examples/claude_desktop_config.json`): ```json { "mcpServers": { "mcpfabric": { "command": "node", "args": ["/absolute/path/to/mcpfabric/mcp-server/dist/index.js"], "env": { "MCPFABRIC_URL": "http://127.0.0.1:25599", "MCPFABRIC_TOKEN": "paste-the-token-from-the-mod-log" } } } } ``` ### Claude Code Use the `.mcp.json` in the project root (see `examples/mcp.json`) or: ```bash claude mcp add mcpfabric -- node /absolute/path/to/mcpfabric/mcp-server/dist/index.js ``` Then set `MCPFABRIC_TOKEN` in the server's environment. --- ## Tools (50+) **info** — `get_status`, `list_capabilities` **world (read)** — `get_block`, `get_blocks_region`, `find_blocks`, `get_time_and_weather`, `list_dimensions`, `raycast` **world (write)** — `set_block`, `fill_blocks`, `set_time`, `set_weather` **entities** — `query_entities`, `get_entity`, `summon_entity`, `remove_entity` **players (admin)** — `list_players`, `get_player`, `teleport_player`, `set_gamemode`, `give_item`, `apply_effect`, `message_player`, `kick_player` **command** — `run_command` (any operator-level command, with output capture) **chat** — `send_chat`, `get_recent_chat` **player (local, client)** — `get_self`, `get_inventory`, `get_equipment`, `get_status_effects` **control (client)** — `set_movement`, `stop_movement`, `look`, `look_at`, `jump`, `start_using_item`, `stop_using_item` **interact (client)** — `break_block`, `place_block`, `use_item`, `attack_entity`, `use_entity`, `drop_held_item` **inventory (client)** — `select_hotbar_slot`, `drop_slot`, `swap_slots` **vision (client)** — `screenshot` (PNG for vision models), `describe_scene` **navigation (client)** — `navigate_to` (A\*), `navigation_status`, `stop_navigation` **events** — `poll_events` (recent damage, deaths, chat, spawns, player join/leave) **agent runtime** ([docs/AGENT.md](docs/AGENT.md)) — persistent per-world memory, goals, map and background jobs: `agent_brief`, `observe`, `map_view`, `remember`, `recall`, `memory_update`, `memory_verify`, `goal_add`, `goal_update`, `goal_list`, `plan_craft`, `get_recipes`, `explore_next`, jobs `travel_to` / `explore` / `collect_blocks` / `craft_item` with `job_status` / `job_cancel`, and `open_container` / `container_transfer` / `close_container` Server tools require a running server (integrated on the client or dedicated). Client tools (`control` / `interact` / `vision` / `navigation` / `player` / `inventory`) only work on the client. Call `get_status` first — it reports which side you are on and which groups are available. --- ## Example prompts - "Look around and describe what's nearby" → `get_self` + `describe_scene` (+ `screenshot` for a vision model). - "Walk to these coordinates and mine diamonds" → `find_blocks` → `navigate_to` → `break_block`. - "Get a stone pickaxe" → `plan_craft` → `collect_blocks` (logs, stone) → `craft_item`; progress is kept in the goal tree and memory, so a later session resumes with `agent_brief`. - "What's happening on the server" → `list_players` + `poll_events`. - "Build a wall" → `fill_blocks` or a series of `set_block` / `run_command`. --- ## Security - The bridge listens on **`127.0.0.1` only** and requires a **bearer token**. - Operator-level capabilities (`run_command`, world writes, player control) are **on by default** — this gives the AI full control. Turn off groups with the `enable*` flags if you need to. - Do not expose `host` externally without understanding the risk and putting an authenticated reverse proxy in front of it. See [SECURITY.md](SECURITY.md). --- ## Project structure ``` mcpfabric/ ├─ settings.gradle, stonecutter.gradle # Stonecutter nodes (version × loader) ├─ build.gradle, build.neoforge.gradle # Fabric Loom / NeoForge ModDevGradle builds ├─ gradle/common.gradle, gradle/modrinth.gradle # shared by both loaders ├─ gradle.properties # shared build config ├─ versions/<node>/gradle.properties # per-node Minecraft + loader versions ├─ src/main/java/dev/mcpfabric/ # common (env *): bridge + server handlers │ ├─ McpFabric.java, ServerHolder.java │ ├─ platform/ (Platform: the loader services the shared code needs) │ ├─ fabric/, neoforge/ (loader entrypoints; only the node's own loader is compiled) │ ├─ bridge/ (HttpBridgeServer, RpcRouter, MainThread, SseHub, Json, ...) │ ├─ config/ (McpConfig) │ ├─ events/ (EventBus, GameEvent) │ └─ handlers/ (Info/World/Entity/PlayerAdmin/Command/Chat + support/CommandRunner, Levels) ├─ src/client/java/dev/mcpfabric/client/ # client (env client): bot + client handlers │ ├─ McpFabricClient.java, ClientMc.java, BotController.java, ClientEvents.java │ ├─ fabric/, neoforge/ (loader client entrypoints) │ ├─ nav/AStarPathfinder.java │ └─ handlers/ (LocalPlayer/Control/Interact/Inventory/Vision/Nav/ClientChat) └─ mcp-server/ # MCP server (TypeScript) ├─ src/index.ts, bridge.ts, tools.ts, config.ts └─ package.json, tsconfig.json ``` See [CONTRIBUTING.md](CONTRIBUTING.md) for the multi-version workflow and how to add a Minecraft version. ## License [MIT](LICENSE).