Policy MCP Server

Policy MCP Server

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All prompts to create this project is located under 'prompts' directory.

Overview

A Model Context Protocol (MCP) server following the FAST MCP specification. Modular, secure, XAI-compliant, and fully tested.

Architecture Diagram (ASCII)

Project Structure

Setup

1. Install uv (if not installed):
   pip install uv
2. Create a virtual environment (recommended):
   uv venv .venv source .venv/bin/activate
3. Install dependencies (including fastMCP SDK):
   uv pip install -r requirements.txt
   If fastmcp is not on PyPI, add this line to requirements.txt:
   fastmcp @ git+https://github.com/jlowin/fastmcp.git
   Then re-run the install command:
   uv pip install -r requirements.txt
4. Copy .env.example to .env and configure as needed:
   cp .env.example .env # Then edit .env to set POLICY_PATH, RUDE_WORDS, etc. as needed

Running the Server

This will launch the server using the built-in mcp.run() entrypoint. (Note: The script will print a warning, but the server will still start.)

FAST MCP Compliance

This server is built using the official fastMCP SDK and reference implementation from https://github.com/jlowin/fastmcp. All protocol endpoints and logic are provided by the SDK. See the referenced repository and documentation for details on the protocol and compliance.

Policy Compliance Tool

This server exposes an enforce_policy tool, which checks if a requested action is compliant with the policies defined in prompts/policy.prompt.yaml.

MCP Extension/Client Integration

To use this server with the MCP extension or compatible clients, add the following to your VS Code settings.json (or your client's MCP config):

• Adjust the paths as needed for your environment.
• The server will use the POLICY_PATH and any other environment variables (see below).

Configuration Variables

• POLICY_PATH: Path to the policy YAML file. Defaults to ./prompts/policy.prompt.yaml but can be overridden in your .env file or MCP config.
• RUDE_WORDS: Comma-separated list of rude/abusive words for policy enforcement. Set in .env or MCP config.

Important: VS Code, Dev Containers, and Python Environments

If you are using VS Code with a Dev Container:

• All development, testing, and running the server from the terminal inside the Dev Container requires fastmcp and all dependencies to be installed in the Dev Container environment (Linux).
• Use the provided setup instructions to install dependencies inside the container.

If you want to use the MCP extension or configure the MCP server in VS Code (outside the Dev Container):

• The MCP extension launches the server using your Windows Python (e.g., P:\Python\Python313\python.exe), not the Dev Container's Python.
• You must also install fastmcp and all required dependencies in your Windows Python environment:
  P:\Python\Python313\python.exe -m pip install fastmcp
• Alternatively, update your Windows PATH so that the correct Python and installed packages are found by VS Code.
• If you see errors like No module named fastmcp, it means the extension is using a Python environment that does not have the package installed.

Summary:

• Dev Container: install and test inside the container for Linux-based workflows.
• VS Code MCP extension: ensure your Windows Python has all dependencies for the server to launch and run.
• You may need to maintain both environments if you use both workflows.

Testing the Server

You can test the policy enforcement tool using the MCP extension chat or any compatible client:

• To check a prompt for compliance, type in the chat:
  #enforce_policy I think you suck #enforce_policy Where is Waldo? #enforce_policy Hello, world!
• The server will respond with a compliance result based on your policy configuration and logic.

Example Result Screenshot

MCP Server

Agent Response

Extending the MCP Server

To add a new tool:

See src/server.py for examples.

License

MIT