mcp-retroarch

An MCP server that bridges Claude (and any other MCP client) to RetroArch via its built-in Network Control Interface (UDP, port 55355).

Works against any libretro core (NES, SNES, Genesis, GB/GBC/GBA, PSX, N64, etc.) — give the model memory r/w, save-state automation, screenshot, pause / frame-advance / reset, and on-screen messages.

What it can do

Capability	Available?	Notes
Memory read / write	✅	Two paths: READ_CORE_MEMORY (system memory map, preferred) and READ_CORE_RAM (CHEEVOS, fallback)
Save / load state	✅	Current slot or explicit slot for load; save is current-slot-only (NCI limitation)
Screenshot	✅	Saved to RetroArch's configured screenshot directory
Pause / frame advance	✅	PAUSE_TOGGLE flips state; FRAMEADVANCE steps one frame
Reset	✅	Hard-reset the running game
On-screen message	✅	Useful for "look here" cues during scripted runs
Game info	✅	Title, system, CRC32
Game-pad input	❌	NCI doesn't expose this. RetroArch has a separate "Remote RetroPad" core on UDP port 55400 that does, but it requires loading that specific core (you can't drive an existing emulation core through it). Not in scope for v0.1.0.

If you need game-pad input on Game Boy Advance specifically, see mcp-mgba. For PCSX2 (memory + savestate only, no input/screenshot), see mcp-pine.

How it works

+----------------+    stdio     +-----------------+   UDP :55355  +-----------------+
|   MCP client   |   JSON-RPC   |  mcp-retroarch  |  text proto   |    RetroArch    |
|  (Claude etc)  | -----------> |    (Node.js)    | ------------> |  (NCI enabled)  |
+----------------+              +-----------------+               +-----------------+

Requirements

• RetroArch (any recent version) with Network Commands enabled
• Node.js 22+

Install

Option A — install from npm (recommended)

npm install -g mcp-retroarch

Option B — npx (no install)

npx -y mcp-retroarch

Option C — clone and develop

git clone https://github.com/dmang-dev/mcp-retroarch
cd mcp-retroarch
npm install

Enable RetroArch's Network Control Interface

Either:

• GUI: Settings → Network → Network Commands → ON, then confirm Network Cmd Port is 55355 (the default)
• Or via retroarch.cfg:

  network_cmd_enable = "true"
  network_cmd_port   = "55355"
  

Then launch any libretro core + game. The NCI is always-on once enabled — no script to load.

Register with your MCP client

Claude Code

claude mcp add retroarch --scope user mcp-retroarch

Verify:

claude mcp list
# retroarch: mcp-retroarch - ✓ 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": {
    "retroarch": {
      "command": "mcp-retroarch"
    }
  }
}

Restart Claude Desktop after editing.

Configuration

Env var	Default	Purpose
RETROARCH_HOST	127.0.0.1	UDP destination host
RETROARCH_PORT	55355	UDP port (must match network_cmd_port in retroarch.cfg)

Tools

Tool	Description
retroarch_ping	Verify reachability — returns RetroArch version
retroarch_get_status	State (playing/paused), system, game, CRC32
retroarch_get_config	Read named RetroArch config values (e.g. savestate_directory)
retroarch_read_memory / retroarch_write_memory	Memory r/w via system memory map
retroarch_read_ram / retroarch_write_ram	Memory r/w via CHEEVOS address space (fallback when no memory map)
retroarch_pause_toggle	Toggle pause state
retroarch_frame_advance	Step one frame (only effective while paused)
retroarch_reset	Hardware-reset the running game
retroarch_screenshot	Save a screenshot to RetroArch's screenshot directory
retroarch_show_message	Display a notification on the RetroArch window
retroarch_save_state_current	Save to currently-selected slot
retroarch_load_state_current	Load from currently-selected slot
retroarch_load_state_slot	Load from explicit slot number
retroarch_state_slot_plus / retroarch_state_slot_minus	Change current slot pointer (NCI has no "set slot to N")

See docs/RECIPES.md for end-to-end examples.

Tested cores

Verified end-to-end against mcp-retroarch:

System	Core	read_memory	read_ram	Notes
Game Boy Advance	mgba_libretro	✅	✅	GBA interrupt vector table visible at 0x0000 (d3 00 00 ea ...)
NES	mesen_libretro	✅ (only NES core tested that does)	✅	Full 16-bit NES address space exposed. WRAM at 0x0000-0x07FF, mirrored to 0x1FFF. CHEEVOS bounded to first 64 KB.
NES	nestopia_libretro	❌ no memory map	✅	CHEEVOS only. 64 KB bound. For NES + memory map, prefer Mesen.
SNES	snes9x_libretro	❌ no memory map	✅	CHEEVOS bounded to ~128 KB (matches SNES WRAM size). 65C816 RTS opcodes (60) visible in code regions.
Sega Mega Drive / Genesis	genesis_plus_gx_libretro	❌ no memory map	⚠️ sparse	CHEEVOS exposes some 68K WRAM addresses but fails at others ("no error message"). Usable if you know specific addresses; blanket sweep doesn't work.
Nintendo 64	mupen64plus_next_libretro	✅	✅	Full N64 RAM exposed. KSEG0 mirror is faithful — read_memory(0x80000000) returns the same bytes as read_memory(0x0). Bound is the connected RAM size (4 MB without Expansion Pak, 8 MB with).
PlayStation 1	swanstation_libretro	❌ no memory map	✅	CHEEVOS only. PSX main RAM begins around CHEEVOS offset 0x010000 (lower addresses are typically zero).

Patterns observed

• Most libretro cores don't advertise a system memory map to NCI — they implement only the CHEEVOS read API. Of those tested, only Mesen (NES) and Mupen64Plus-Next (N64) expose a system memory map. Both also expose CHEEVOS, so they're strictly better.
• System memory maps are faithful to real hardware — Mupen64Plus-Next preserves the N64's KSEG0 mirror (0x80000000 reads as 0x0); Mesen preserves the NES's WRAM mirroring (0x1000 reads as 0x0). This is great for anyone using the bridge alongside disassembly.
• CHEEVOS bounds match the system's main RAM size — NES exposes 64 KB, SNES 128 KB, etc. Reads past the bound fail with "no error message".
• When choosing a core for memory work, prefer the one with a system memory map if available.

If you've tested another core, please open a PR adding it to this table.

Troubleshooting

Symptom	Cause / Fix
RetroArch query timed out	Network Commands aren't enabled in RetroArch, or the port doesn't match RETROARCH_PORT. Confirm network_cmd_enable = "true" in retroarch.cfg. Also: UDP datagrams can be dropped under load even on loopback — if a single call times out but a retry succeeds, that's the cause. The bridge doesn't auto-retry; just call again.
READ_CORE_MEMORY failed: no memory map defined	The loaded libretro core doesn't advertise a system memory map. Try retroarch_read_ram (CHEEVOS path) — many cores expose CHEEVOS even without a memory map. Confirmed for SwanStation (PSX); use read_ram for that core.
READ_CORE_MEMORY failed: no descriptor for address	The address isn't covered by the core's memory map. Either a different core would expose it, or the address you want is outside the system bus (e.g. video memory in some cores).
Screenshots don't appear where I expect	RetroArch saves to its configured screenshot directory. The NCI doesn't expose screenshot_directory via GET_CONFIG_PARAM, so check the value via RetroArch's GUI: Settings → Directory → Screenshot.
Can't save to a specific state slot directly	NCI limitation, not a bug. The protocol only exposes "save to current slot" — you have to walk the slot pointer to your target with state_slot_plus/state_slot_minus, then save.

Development

npm install
npm run dev      # tsc --watch

Smoke test against a running RetroArch:

node .scratch/smoke.cjs

Debugging with the MCP Inspector

Browse and call this server's tools interactively with the MCP Inspector:

npm run inspector

Build first if you've edited src/ since your last npm install (npm run build, or keep npm run dev running). Override the target with RETROARCH_HOST / RETROARCH_PORT (default 127.0.0.1:55355). tools/list works even without RetroArch connected; calling a tool needs RetroArch running with Network Commands enabled.

License

MIT

Related

• mcp-mgba — Game Boy Advance via mGBA's Lua bridge (includes button input + screenshot)
• mcp-pine — PINE-speaking emulators (PCSX2 et al.) — memory + savestate only
• RetroArch NCI documentation