STS2MCP

An Experimental Research Project to Fully-Automate your Slay the Spire 2 Runs

A mod for Slay the Spire 2 that lets AI agents play the game. Exposes game state and actions via a localhost REST API, with an optional MCP server for Claude Desktop / Claude Code integration.

Singleplayer and multiplayer (co-op) supported, plus full menu and lobby control: profile switching, character select (SP and MP host/client) with optional seed, multiplayer host / Steam-friend join / FastMP localhost join, multiplayer load lobby for resuming saved co-op runs, game-over dismissal, FTUE/tutorial popup handling, and Timeline visibility. Tested against STS2 v0.103.2.

[!warning] This mod allows external programs to read and control your game via a localhost API. Use at your own risk with runs you care less about.

[!caution] Multiplayer support is in beta — expect bugs. Any multiplayer issues encountered with this mod installed are very likely caused by the mod, not the game. Please disable the mod and verify the issue persists before reporting bugs to the STS2 developers.

For Players

1. Install the Mod

Grab the latest release and follow the instructions:

1. Copy STS2_MCP.dll and STS2_MCP.json to <game_install>/mods/
2. Launch the game and enable mods in settings (a consent dialog appears on first launch)
3. The mod starts an HTTP server on localhost:15526 automatically

[!note] The release DLL is a platform-agnostic .NET assembly — the same STS2_MCP.dll and STS2_MCP.json work on Windows, Linux, and macOS. No separate builds are needed.

macOS install

On macOS, the mods directory lives inside the app bundle. The default Steam install path is:

~/Library/Application Support/Steam/steamapps/common/Slay the Spire 2/
    SlayTheSpire2.app/Contents/MacOS/mods/

To install, right-click SlayTheSpire2.app → Show Package Contents, navigate to Contents/MacOS/, and create a mods folder. Or from the terminal:

GAME_DIR="$HOME/Library/Application Support/Steam/steamapps/common/Slay the Spire 2"
MODS_DIR="$GAME_DIR/SlayTheSpire2.app/Contents/MacOS/mods"
mkdir -p "$MODS_DIR"
cp STS2_MCP.dll "$MODS_DIR/"
cp STS2_MCP.json "$MODS_DIR/"

Launch the game and open Settings → Mods. The mod should appear in the list. A consent dialog appears on first launch — accept it to enable mod loading. Once enabled, verify the HTTP server is running:

curl -s http://localhost:15526/

A successful response looks like:

{"message": "Hello from STS2 MCP v0.3.4", "status": "ok"}

If you get "Connection refused", the mod is not loaded — check that mods are enabled in the game's settings.

2. Give Your AI Instructions to Interact with the Game

Clone or download the repository, then:

I prefer a skill	I prefer an MCP Server
Tell AI to reference docs/raw-*.md. Sit back, and watch it play.	Requires Python 3.11+ and uv. Follow the instructions below ⬇️

MCP server setup

Install uv if you don't have it (macOS: brew install uv). Then run the server once to install dependencies:

uv run --directory /path/to/STS2_MCP/mcp python server.py --help