mcp-bizhawk

An MCP server that exposes BizHawk — the multi-system emulator the TAS community lives in — to any MCP-compatible client (Claude Desktop, Claude Code, etc.).

One bridge, many systems: NES, SNES, Game Boy / GBC / GBA, Sega Master System / Genesis / 32X / Saturn, N64, PlayStation 1, Atari 2600/5200/7800, Lynx, ColecoVision, Intellivision, and more — all through the same MCP tools, with per-system memory domains exposed cleanly.

How it works

+------------------+    stdio     +------------------+   TCP :8766   +------------------+
|   MCP client     |   JSON-RPC   |    mcp-bizhawk   |  newline JSON |     BizHawk      |
| (Claude / etc.)  | ===========> |     (Node.js)    | <============ |    bridge.lua    |
+------------------+              +------------------+               +------------------+

The transport is inverted compared to most other emulator-MCP bridges: BizHawk's Lua doesn't have native server sockets, only an outbound comm.socketServer* client. So mcp-bizhawk runs the TCP listener, and BizHawk's Lua bridge dials in once per frame to ferry commands and replies.

Two pieces:

• lua/bridge.lua — runs inside BizHawk's Lua Console, polls our TCP server once per frame

• dist/index.js — the Node.js MCP server, listens on 127.0.0.1:8766 by default, exposes tools over stdio

Trade-off: this design adds ~one frame of latency per call (≈16ms at 60Hz). Fine for interactive memory hunting, save-state experimentation, and frame-by-frame inspection. Less ideal for high-rate-of-fire scripting.

Related MCP server: mcp-retroarch

Requirements

• BizHawk 2.6.2 or newer (earlier builds use an older socket-server wire format)

• Node.js 18+ (for the MCP server)

Tested on BizHawk 2.11.1 across SNES (Super Metroid). Should work on any system BizHawk supports.

Install

Option A — install from npm (recommended)

npm install -g mcp-bizhawk

Option B — npx (no install)

npx -y mcp-bizhawk

Option C — clone and develop

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

Set up the BizHawk bridge

There are two pieces to configure: telling BizHawk where to connect, and loading the bridge script.

1. Point BizHawk at the MCP server

Easiest: launch BizHawk with the socket flags directly.

EmuHawk.exe --socket_ip=127.0.0.1 --socket_port=8766 <path/to/rom>

(Adjust port if you're overriding BIZHAWK_PORT.)

Alternative: configure persistently via Settings → Customize → External Tools in BizHawk's UI.

2. Load the bridge script

In BizHawk: Tools → Lua Console → Open Script → select lua/bridge.lua from this repo.

You should see in the Lua Console:

[mcp-bizhawk] bridge starting
[mcp-bizhawk] socket server target: 127.0.0.1:8766
[mcp-bizhawk] socket receive timeout set to 50ms
[mcp-bizhawk] frame loop active — bridge is polling once per frame

And in the mcp-bizhawk process's stderr:

[mcp-bizhawk] BizHawk client connected (waiting for bridge.lua to start polling)
[mcp-bizhawk] bridge.lua is polling — bridge ready

Register with your MCP client

Claude Code (CLI)

claude mcp add bizhawk --scope user mcp-bizhawk

Verify:

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

Claude Desktop

Edit claude_desktop_config.json:

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

Restart Claude Desktop after editing.

Other MCP clients

The server speaks standard MCP over stdio. Run mcp-bizhawk and connect any MCP client to its stdio.

Configuration

Tools

All memory r/w tools take an optional domain parameter — if omitted, the active "current" memory domain is used. Use bizhawk_list_memory_domains to discover the names available on the loaded core.

See docs/RECIPES.md for end-to-end examples (RAM hunting on SNES/NES/N64, frame-precise input, snapshot-experiment-restore, cross-system regression testing) and CHANGELOG.md for release history.

Memory domains by system (cheat sheet)

Names come straight from BizHawk's core implementation. Use bizhawk_list_memory_domains to see the exact set for the loaded ROM.

Buttons by system

BizHawk's joypad.set takes a {ButtonName=true, ...} table where button names depend on the core. Common ones:

If you're unsure, run a probe: bizhawk_press_buttons {"A": true} and watch the active core's input display in BizHawk.

Troubleshooting

Development

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

End-to-end smoke test (launches BizHawk, loads ROM + bridge, runs ping/get_info/list_memory_domains/read_range):

node .scratch/test-all.cjs "I:\path\to\your\rom.smc"

Set DEBUG=1 to dump every RX/TX line.

License

MIT