STS2 AI Agent: a Slay the Spire 2 mod with MCP
STS2 AI Agent
A Slay the Spire 2 mod with built-in MCP: an external agent reads the combat state and picks the actions itself
- 351 ★ on the repository
- Last commit
Extended access
Why this level
- The mod opens a local HTTP API and MCP through which an external agent controls the game
- The API key of your model is kept in the mod settings, and request text goes to the chosen provider
Install
- Works in
Manual install
{"mcpServers": {"sts2-ai-agent": {"type": "http", "url": "http://127.0.0.1:8080/mcp"}}}First turn on Open MCP service on the Connect tab and substitute the real port.
Access and checks
How we reviewExtended accessThe tool runs code or makes network calls and only reads external data.
- The mod opens a local HTTP API and MCP through which an external agent controls the game
- The API key of your model is kept in the mod settings, and request text goes to the chosen provider
This is third-party code. Review the repository files before installing.
What it does
STS2 AI Agent is a mod for Slay the Spire 2 that exposes the game state and allowed actions through a local HTTP API. The settings window opens with the F8 key right inside the game. There you set the address and model of any OpenAI-compatible API, Ollama and LM Studio included. The model plays the fights itself, picks rewards and the route, and handles events and shops. The mod can launch a second game instance with an AI teammate for co-op: you play your character while the teammate controls its own and answers chat messages. Session tokens and request counts are shown on screen, and once the limit is reached the mod stops calling the model. The Connect tab turns on the built-in MCP at /mcp on the same port. It is off by default and listens on 127.0.0.1 only. An external agent in Cursor, Claude or Codex gets tools such as get_game_state, get_available_actions and act, and the guided profile holds 17 tools. For external agents the repository ships the sts2-mcp-player skill with gameplay rules.
Who it is for. For players and developers who want to play Slay the Spire 2 with an AI or hand the game to an agent from Cursor, Claude Code or Codex.
Good fit when
- You want a Slay the Spire 2 co-op run where an AI teammate is the second player
- You want to see how a chosen language model handles a turn-based game without manual hints
- An agent in Cursor or Claude Code should read the combat state and call actions over MCP
- You need a local model through Ollama or LM Studio with no API key
- For research you want the decision log and run summary that get_decision_log and get_run_summary return
Not a fit when
- You do not own Slay the Spire 2: the mod works only inside this game
- You play without mods: the mod starts from Steam with Play with Mods
- You need a guaranteed result: play quality and run completion depend on the model and conditions
- Game-state text must not go to an outside model provider: auto-play passes it to the API you chose
Example request
Check the combat state through sts2-ai-agent, choose a move for the current hand and explain why.MCP
- Transport
- http, stdio
- Authentication
- not required
Limitations
The mod is in development and some parts may be unfinished. Installed from the Steam Workshop and by hand at the same time, it loads twice.
Auto-play needs a configured model and a passing connection test, and even a working chat does not guarantee the model can play. Tool calling, vision and streaming depend on the provider. Token counters and session budgets do not replace the provider's bill. Whether Western providers are reachable from Russia has not been checked.
The MCP port can differ from 8080, so take the address from the Connect tab. The Python proxy in the mcp_server folder is for developers only. The project is licensed under AGPL-3.0.
How to disable. Unsubscribe from the mod in the Steam Workshop or delete the three STS2AIAgent files from the game's mods folder. The built-in MCP can also be turned off on the Connect tab.
FAQ
How do I install the STS2 AI Agent mod?
The easiest way is the Steam Workshop page: subscribe, wait for the download and start the game with Play with Mods. From GitHub copy three files into the mods folder: STS2AIAgent.dll, STS2AIAgent.pck and mod_id.json.
How do I connect the mod to Claude Code or Cursor?
Press F8, open the Connect tab and turn on Open MCP service. Copy the address or JSON the tab shows and add a server of type http to the client configuration.
What is the sts2-mcp-player skill for?
It holds the gameplay rules with which an external agent plays as well as the built-in auto-play. Without the skill an agent can click legal actions, but play quality will be lower.
How do I play with an AI teammate?
In the main menu open the AI Teammate tab and click Invite AI Teammate. A second game window launches and joins the co-op lobby, and you can talk in chat.
Does the mod need Python?
No. Python and uv are needed only for the optional mcp_server proxy, which adds stdio and the layered and full profiles. Players and the built-in MCP do not need it.
Discussion
No questions or reviews yet.
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Comparison with similar tools
Entries that share the main search query, and how they differ.
| Entry | Official | Authentication | Repository stars | Main difference |
|---|---|---|---|---|
| STS2 AI Agent: a Slay the Spire 2 mod with MCP (this entry) | no | not required | 351 | |
| Minecraft MCP Server | no | not required | 799 | the agent controls a bot in Minecraft; here it plays the cards and turns of Slay the Spire 2 |
| STS2MCP | no | not required | 535 | a Slay the Spire 2 mod and MCP server that let Claude Code or Claude |
README in short
The documentation takes a player from installing the mod through three scenarios: auto-play, co-op with a teammate and handing the teammate window to an external agent. Separate sections explain which MCP entry to choose, the repository layout and building from source.