mcp-mgba

An MCP server that exposes the mGBA Game Boy Advance emulator to any MCP-compatible client (Claude Desktop, Claude Code, etc.).

Lets your model read and write GBA memory, inject button presses, take screenshots, and step the emulator — all through a clean tool interface.

Claude driving an in-development homebrew side-scroller through mgba_press_buttons — Start to begin, A to confirm New Game, then Right to walk and A to jump. Each frame is captured via mgba_screenshot.

How it works

+------------------+    stdio     +------------------+   TCP :8765   +------------------+
|   MCP client     |   JSON-RPC   |     mcp-mgba     |  newline JSON |  mGBA emulator   |
| (Claude / etc.)  | ===========> |     (Node.js)    | ============> |    bridge.lua    |
+------------------+              +------------------+               +------------------+

Two pieces:

• lua/bridge.lua — runs inside mGBA's scripting engine, opens a loopback TCP server on port 8765
• dist/index.js — Node.js MCP server, talks to the Lua bridge over TCP, exposes tools over stdio

Requirements

• mGBA 0.10 or newer (with Lua scripting)
• Node.js 18+ (for the MCP server)

Install

Option A — install from npm (recommended)

npm install -g mcp-mgba

Puts mcp-mgba on your PATH. Verify with mcp-mgba --help (it'll print a startup line and wait for stdio — Ctrl+C to exit).

Option B — npx (no install)

npx -y mcp-mgba

Run on demand. Good for trying it out without committing to a global install.

Option C — clone and develop

git clone https://github.com/dmang-dev/mcp-mgba
cd mcp-mgba
npm install        # also runs the build via the `prepare` hook

Then reference the absolute path to dist/index.js when registering, or npm install -g . to symlink the bin globally.

Set up the mGBA bridge

1. Launch mGBA and load any GBA ROM.
2. Open Tools > Scripting…
3. Click File > Load script and select lua/bridge.lua from this repo.

You should see in the scripting console:

[mcp-mgba] bridge listening on 127.0.0.1:8765
[mcp-mgba] frame callback registered — bridge is active

If you see a bind failed error, the previous instance's socket is still held — quit and relaunch mGBA.

Register with your MCP client

Claude Code (CLI)

claude mcp add mgba --scope user mcp-mgba

(if you used Option B without global install, replace mcp-mgba with node /absolute/path/to/dist/index.js)

Verify:

claude mcp list
# mgba: mcp-mgba - ✓ Connected

Claude Desktop

Edit claude_desktop_config.json:

| Platform | Path | |---|---| | macOS | ~/Library/Application Support/Claude/claude_desktop_config.json | | Windows | %APPDATA%\Claude\claude_desktop_config.json | | Linux | ~/.config/Claude/claude_desktop_config.json |

Add (assuming Option A — globally installed):

{
  "mcpServers": {
    "mgba": {
      "command": "mcp-mgba"
    }
  }
}

Or with explicit Node + path (Option B):

{
  "mcpServers": {
    "mgba": {
      "command": "node",
      "args": ["/absolute/path/to/mcp-mgba/dist/index.js"]
    }
  }
}

Restart Claude Desktop after editing.

Other MCP clients

The server speaks standard MCP over stdio. Run mcp-mgba (or node dist/index.js) and connect any MCP client to its stdio.

Configuration

| Env var | Default | Purpose | |-------------|---------------|------------------------| | MGBA_HOST | 127.0.0.1 | Bridge host to dial | | MGBA_PORT | 8765 | Bridge port to dial |

Tools

| Tool | Description | |------|-------------| | mgba_ping | Verify bridge connectivity (returns pong) | | mgba_get_info | Game title, code, frame count | | mgba_read8 / mgba_read16 / mgba_read32 | Read memory at an address | | mgba_write8 / mgba_write16 / mgba_write32 | Write to RAM | | mgba_read_range | Read up to 4096 bytes as a byte array | | mgba_write_range | Write up to 4096 bytes from a byte array | | mgba_press_buttons | Queue a button press (FIFO; consecutive calls produce distinct events) | | mgba_advance_frames | Step the emulator N frames | | mgba_pause / mgba_unpause | Pause / resume emulation | | mgba_reset | Reset the loaded ROM | | mgba_screenshot | Save a PNG of the current display | | mgba_save_state / mgba_load_state | Save/load emulator state to a slot or path |

See docs/RECIPES.md for end-to-end examples (RAM hunting, snapshot-experiment-restore, side-scroller automation, etc.).

GBA button names

A, B, Select, Start, Right, Left, Up, Down, R, L

GBA address space (cheat sheet)

| Range | Region | |----------------|-------------------------------| | 0x02000000 | EWRAM (256 KiB, general) | | 0x03000000 | IWRAM (32 KiB, fast) | | 0x04000000 | I/O registers | | 0x05000000 | Palette RAM | | 0x06000000 | VRAM | | 0x07000000 | OAM | | 0x08000000 | ROM (read-only) |

Troubleshooting

| Symptom | Cause / Fix | |---|---| | Cannot reach mGBA bridge at 127.0.0.1:8765 | mGBA isn't running, or bridge.lua isn't loaded — open Tools > Scripting and load it | | bind failed — port 8765 may already be in use | A previous mGBA instance still holds the socket; quit and relaunch mGBA | | Tool calls hang | The bridge script may have errored out silently after a hot-reload — check the mGBA scripting console | | Tools missing in Claude after install | Restart your MCP client; Claude only enumerates servers on startup | | Tool calls return data shaped like an old version after editing bridge.lua and choosing Load Script again | mGBA doesn't fully tear down a previous script when you reload. The new script's bind() may succeed but the old frame callback keeps serving requests. Fix: quit mGBA entirely, relaunch, load the ROM, then load bridge.lua once. Check the console for the frame callback registered line — there should be exactly one. | | attempt to index a nil value (global 'emu') at script load | mGBA's emu global only exists once a ROM is loaded. Load any ROM first, then load bridge.lua. (Or load the script first; capability detection will defer until a ROM is loaded.) | | emu:foo not available on this mGBA build for pause, unpause, frameAdvance, etc. | This particular build of mGBA doesn't expose that method. The bridge feature-detects on the first frame; check mgba_get_info for the full capabilities map. For frameAdvance, the bridge falls back to runFrame then step automatically. | | read8/16/32 returns "invoking failed" intermittently | Known mGBA Lua quirk — the typed read methods are flaky via pcall from the frame callback. The bridge already routes read8/16/32 through the more reliable readRange internally; if you still see this on a write, the retry loop usually clears it within a few attempts. | | Multiple press_buttons calls don't seem to register as distinct events | Older mgba_press_buttons (≤0.1.0) had this bug; v0.2.0+ uses a FIFO queue. Make sure you've upgraded with npm install -g mcp-mgba and restarted your MCP client. |

Development

npm install
npm run dev      # tsc --watch — autobuilds on src/ changes

The Lua side (lua/bridge.lua and lua/json.lua) needs no build step. Edit and reload via mGBA's File > Load script.

License

MIT