mcp-mgba

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 22+ (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

• Launch mGBA and load any GBA ROM.
• Open Tools > Scripting…
• 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