etoryx/mcpfabric

[!IMPORTANT] This repository has moved to denfry/mcpfabric. All development, releases, issues and pull requests continue there. This copy is no longer updated. Downloads stay on Modrinth. Please open new issues and PRs in the new repository.

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 and Fabric API, or NeoForge.
2. Download the jar matching your Minecraft version and loader from Modrinth 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.

[!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. Each version below ships its own jar:

14 Fabric jars are produced, each named mcpfabric-+.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-+.jar:

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

# 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 -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//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.

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)

{
  "host": "127.0.0.1",
  "port": 25599,
  "token": "generated automatically",
  "requireAuth": true,
  "callTimeoutMs": 8000,
  "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.

---

2. MCP server

cd mcp-server
npm install
npm run build      # compiles to dist/

Usually your MCP client launches it for you (see below). Manually:

MCPFABRIC_URL=http://127.0.0.1:25599 MCPFABRIC_TOKEN= node dist/index.js

Environment variables

---

3. Connect to Claude

Claude Desktop

claude_desktop_config.json (see examples/claude_desktop_config.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:

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) — 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.

---

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//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 for the multi-version workflow and how to add a Minecraft version.

License

MIT.