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.

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:

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

{
  "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

Env var	Default	Purpose
BIZHAWK_HOST	127.0.0.1	TCP host to listen on for BizHawk
BIZHAWK_PORT	8766	TCP port to listen on for BizHawk

Tools

Tool	Description
bizhawk_ping	Verify bridge connectivity (returns pong)
bizhawk_get_info	ROM name, ROM hash, framecount, memory domains, capabilities
bizhawk_list_memory_domains	List available memory domains for the loaded core
bizhawk_read8 / bizhawk_read16 / bizhawk_read32	Read u8 / u16-LE / u32-LE from memory
bizhawk_write8 / bizhawk_write16 / bizhawk_write32	Write to memory
bizhawk_read_range	Read up to 4096 bytes as a byte array
bizhawk_write_range	Write up to 4096 bytes from a byte array
bizhawk_press_buttons	Set joypad state for one player; keys are button names, values booleans
bizhawk_frame_advance	Step the emulator by N frames
bizhawk_pause / bizhawk_unpause	Pause / resume emulation
bizhawk_reset	Reset the loaded core
bizhawk_screenshot	Save a PNG of the current display to a path
bizhawk_save_state / bizhawk_load_state	Save / load emulator state to a file path

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.

System	Main RAM domain	Other common domains
NES	RAM	PPU, OAM, PRG ROM, CHR
SNES	WRAM	VRAM, CARTROM, CARTRAM
GB/GBC	WRAM	VRAM, HRAM, OAM, ROM
GBA	EWRAM, IWRAM	VRAM, PALRAM, OAM, ROM
Genesis	68K RAM	VRAM, Z80 RAM, CARTRAM
N64	RDRAM	SP DMEM, SP IMEM, PI Reg
PSX	MainRAM	VRAM, Scratchpad, BIOS

Buttons by system

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

System	Names
NES	A, B, Up, Down, Left, Right, Start, Select
SNES	A, B, X, Y, L, R, Up, Down, Left, Right, Start, Select
GB/GBC	A, B, Up, Down, Left, Right, Start, Select
GBA	A, B, L, R, Up, Down, Left, Right, Start, Select
N64	A, B, Z, L, R, Start, Up, Down, Left, Right, C-Up, C-Down, C-Left, C-Right
Genesis	A, B, C, X, Y, Z, Up, Down, Left, Right, Start, Mode

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

Troubleshooting

Symptom	Cause / Fix
MCP tool calls hang for 10 seconds, then time out with "is the bridge.lua script still polling?"	bridge.lua isn't loaded. In BizHawk: Tools → Lua Console → Open Script → bridge.lua. Check the console for frame loop active.
BizHawk connects to the server but tool calls still time out	You're on BizHawk older than 2.6.2 — the socket wire format changed then. Upgrade BizHawk.
[mcp-bizhawk] FATAL: comm.socketServer* not available in the Lua Console	BizHawk wasn't launched with --socket_ip / --socket_port flags, and no socket server is configured in Settings → Customize → External Tools.
Tools missing in Claude after install	Restart your MCP client; Claude only enumerates servers on startup.
Memory reads return zeros for the first few seconds after boot	The emulator hasn't initialized RAM yet. Either advance some frames (bizhawk_frame_advance) or check bizhawk_get_info to confirm framecount > 0 before relying on game state.
unknown memory domain: <name>	The domain name didn't match anything for the loaded core. Call bizhawk_list_memory_domains to see the actual list — names are case-sensitive.
client.screenshot not available or savestate.* not available	Some BizHawk cores expose a slightly different surface. Check bizhawk_get_info — the capabilities map shows which optional functions are present on your current build/core combo.

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