MCP Plugin for .NET

Overview

MCP Plugin for .NET is a comprehensive solution for integrating .NET applications with the Model Context Protocol (MCP). It allows you to easily expose methods and data from your .NET applications as Tools, Prompts, and Resources to AI assistants (like Claude) and other MCP clients.

The Problem: Independent Lifecycles

Standard MCP servers are typically designed to be launched as subprocesses by the client (e.g., Claude Desktop spawns a Python script). This works well for lightweight scripts but creates challenges for complex .NET applications like Unity Engine, WPF Desktop Apps, or Game Servers:

1. Heavy Startup: These applications are often too heavy to be spawned repeatedly by an MCP client.
2. Independent Lifecycle: They often need to run independently (e.g., you are already working in the Unity Editor).
3. Live Context: You want to interact with the currently running instance (e.g., "Add a cube to the current scene"), not start a new, empty instance.

The Solution: The Bridge Pattern

This project solves this by decoupling the MCP Server from your application using a Bridge Architecture:

1. McpPlugin (In-App): A lightweight library you add to your .NET application (e.g., Unity, WPF, Console). It connects to the bridge via SignalR.
2. McpPlugin.Server (Bridge): A high-performance gateway that the MCP Client (Claude) launches. It acts as a persistent mediator.

Why SignalR?

• Resilience: Built-in automatic reconnection logic. If the bridge restarts, your app reconnects instantly.
• Simplicity: Operates over a single HTTP port (default 8080). No complex firewall rules.
• Bidirectional: The bridge can invoke tools in your app, and your app can push updates (logs, progress) back to the bridge.

Architecture

The system uses a hub-and-spoke architecture where McpPlugin.Server acts as the central gateway.

graph LR
    subgraph "Your .NET Apps (SignalR Clients)"
        A[Unity Editor] -- SignalR --> S
        B[WPF Desktop] -- SignalR --> S
        E[Game Server] -- SignalR --> S
    end

    subgraph "MCP Infrastructure (Bridge)"
        S[McpPlugin.Server]
    end

    subgraph "AI / MCP Clients"
        C[Claude Desktop] -- StdIO/HTTP --> S
        D[MCP Inspector] -- StdIO/HTTP --> S
    end

Features

• Attribute-Based Registration: Easily expose tools, prompts, and resources using [McpPluginTool], [McpPluginPrompt], and [McpPluginResource] attributes.
• Powered by ReflectorNet:
  • Complex Type Support: Seamlessly handle nested objects, collections, and custom types in tool parameters.
  • Fuzzy Matching: AI can find and call methods even with partial names or slightly mismatched signatures.
  • **Automatic

... View full README on GitHub