STS2MCP
A Slay the Spire 2 mod and MCP server that let Claude Code or Claude Desktop read the game state and play a run
- 535 ★ on the repository
- Last commit
- MIT
Broad access
Why this level
- The mod opens an API on localhost through which an outside program reads and controls the game
- The agent can switch and delete profile slots, with their progress, using delete_profile
- The mod loads into the game client, so its failures can affect saves and startup
Install
- Works in
In your terminal, with SkillFoxx CLI
npx skillfoxx add mcp/sts2mcpDetects the agents on your machine, shows the access level and pins the version.
Other ways to install
Access and checks
How we reviewBroad accessThe tool can change data, run commands or handle secrets.
- The mod opens an API on localhost through which an outside program reads and controls the game
- The agent can switch and delete profile slots, with their progress, using delete_profile
- The mod loads into the game client, so its failures can affect saves and startup
This is third-party code. Review the repository files before installing.
What it does
STS2MCP has two parts. A Slay the Spire 2 mod starts a local HTTP server on the player's machine that serves game state and accepts commands. The second part is a Python MCP server in the mcp folder that turns this interface into tools for Claude Desktop, Claude Code and other clients. With get_game_state the agent reads the combat state. It then plays cards and potions, ends turns and moves the run along the map. With menu_select it controls menus and the lobby: it picks a character and a seed and starts a solo or co-op game. Other tools read the profile, the compendium and the wiki for discovered cards and relics, and switch profiles. The author calls the project a research experiment: it tests how language models handle a task that is rare for them. The mod runs on Windows, Linux and macOS, and one DLL build fits all systems. Without the MCP server the agent can play from the docs/raw-full.md and docs/raw-simplified.md documents if you hand them over directly.
Who it is for. For players and agent researchers who want to watch Claude play Slay the Spire 2 or test models on games with long chains of decisions.
Good fit when
- You want to compare how different models make decisions in a card game with a long run
- You want to play co-op with an agent: hosting, joining through a Steam friend and a local join are supported
- You need to try an agent idea on a game fast with no interface of your own: state and actions already come as tools
- You need a reference to the cards and relics discovered on your profile for an advisor agent, which search_wiki provides
- You need to connect the game to a client that supports MCP, for example Claude Code through a .mcp.json file
Not a fit when
- You play on an account with runs you care about: the author advises using the project on runs you can afford to lose
- You need stable co-op: multiplayer is still in beta
- You want to report a bug to the game's developers: disable the mod first and check that the bug remains
- You just want to play yourself: a run under an agent's control costs several million tokens
Example request
Call get_game_state, describe what is happening in combat and play a turn that loses as little health as possibleMCP
- Transport
- stdio
- Authentication
- not required
Limitations
- The mod is tested against Slay the Spire 2 version 0.103.2. A game update can break it.
- Multiplayer is in beta. Any issues with the mod installed are most likely caused by it.
- The MCP server needs Python 3.11 or newer and uv. On macOS give the absolute path to uv in the command field, because GUI apps do not inherit PATH.
- The game must be installed. Building the mod from source needs the .NET 9 SDK.
How to disable. Delete STS2_MCP.dll and STS2_MCP.json from the game's mods folder or disable the mod in the game's settings. Remove the MCP server from .mcp.json or claude_desktop_config.json.
FAQ
How do I connect STS2MCP to Claude Code?
Copy STS2_MCP.dll and STS2_MCP.json from the release into the game's mods folder and enable mods in settings. Then add an sts2 server to .mcp.json with the uv command and the arguments run, --directory, the path to the mcp folder, python, server.py. After a restart ask Claude to call get_game_state with the game running.
Where is the mods folder on macOS?
Inside the app bundle: ~/Library/Application Support/Steam/steamapps/common/Slay the Spire 2/SlayTheSpire2.app/Contents/MacOS/mods/. If the folder is missing, create it with mkdir -p. Show Package Contents in Finder opens the bundle.
How many tokens does one run use?
In the author's measurements on the Ironclad, Claude Sonnet 4.6 spends slightly more than 8M tokens on a full run and GPT-5.4 averages 7.34M, tool responses included. Usage depends on the prompt and model.
Is this a cheat mod?
The mod does not change gameplay; it only gives outside programs an interface to the game. What you do with it is up to you. The author stresses that the goal is testing models on a rare task and not replacing players.
How do I check that the mod is running?
Run curl -s http://localhost:15526/. A working mod returns JSON with the message Hello from STS2 MCP and status ok. If you get Connection refused, the mod did not load: check that mods are enabled in the game's settings.
Discussion
No questions or reviews yet.
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README in short
The README splits into sections for players and for developers. Players get mod installation by platform, MCP server setup and a description of the profile and compendium. Developers need the build and the macOS copy steps, and the document ends with a FAQ on the author's motivation and token use.