STS2MCP

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.

Build & Install

Requires .NET 9 SDK and the base game.

PowerShell (recommended):

```powershell

Build instructions for macOS

Install dotnet to compile the mod:

brew install dotnet@9
export DOTNET_ROOT="/opt/homebrew/opt/dotnet@9/libexec"
export PATH="$DOTNET_ROOT:$PATH"

Homebrew installs dotnet@9 as keg-only, so the exports above are required for the current session. Add them to ~/.zshrc to persist across sessions.

Build with dotnet directly (the PowerShell script is Windows-only):

dotnet build STS2_MCP.csproj -c Release -o out/STS2_MCP \
  -p:STS2GameDir="$HOME/Library/Application Support/Steam/steamapps/common/Slay the Spire 2"

On macOS the game ships as an app bundle. The .csproj detects macOS and resolves the data directory to SlayTheSpire2.app/Contents/Resources/data_sts2_macos_arm64 automatically.

The mods directory on macOS lives inside the app bundle at SlayTheSpire2.app/Contents/MacOS/mods/. Finder hides bundle contents by default — to browse it in the GUI, right-click SlayTheSpire2.app → Show Package Contents. Or copy 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 "$MODS_DIR"
cp out/STS2_MCP/STS2_MCP.dll "$MODS_DIR/"
cp mod_manifest.json "$MODS_DIR/STS2_MCP.json"

[!NOTE] mod_manifest.json is renamed to STS2_MCP.json on copy — the game's mod loader expects the manifest filename to match the mod ID.

FAQ

You did not answer the question!

First of all, I play lots of games, including service games that has daily/weekly tasks. I really hoped that modern AI could save me from the grind, which, if you have tried one or more of the GUI agents, never really materialized. Let's face it: modern AI is still pretty bad at gaming because no one cares.

About my intention, as a researcher that loves playing games, the purpose of STS2MCP is to test AI models and agents in a rarely explored (we call it out-of-distribution) domain. Ultimately, this might turn into a benchmark for evaluating the reasoning and decision-making capabilities of different language models.

STS2 is just an example to show how good (or bad) current AI agents are at playing such games. I have no intention to replace human players with AI, and I would definitely rather play STS2 myself as a big fan of the game.