MCPSharp

MCPSharp is a .NET library that helps you build Model Context Protocol (MCP) servers and clients - the standardized API protocol used by AI assistants and models. With MCPSharp, you can:

• Create MCP-compliant tools and functions that AI models can discover and use
• Connect directly to existing MCP servers from C# code with an easy to use client
• Expose your .NET methods as MCP endpoints with simple attributes
• Handle MCP protocol details and JSON-RPC communication seamlessly

🚀 What's New in MCPSharp

• Microsoft.Extensions.AI Integration: MCPSharp now integrates with Microsoft.Extensions.AI, allowing tools to be exposed as AIFunctions
• Semantic Kernel Support: Add tools using Semantic Kernel's KernelFunctionAttribute
• Dynamic Tool Registration: Register tools on-the-fly with custom implementation logic
• Tool Change Notifications: Server now notifies clients when tools are added, updated, or removed
• Complex Object Parameter Support: Better handling of complex objects in tool parameters
• Better Error Handling: Improved error handling with detailed stack traces

When to Use MCPSharp

Use MCPSharp when you want to:

• Create tools that AI assistants like Anthropic's Claude Desktop can use
• Build MCP-compliant APIs without dealing with the protocol details
• Expose existing .NET code as MCP endpoints
• Add AI capabilities to your applications through standardized interfaces
• Integrate with Microsoft.Extensions.AI and/or Semantic Kernel without locking into a single vendor

Features

• Easy-to-use attribute-based API ([McpTool], [McpResource])
• Built-in JSON-RPC support with automatic request/response handling
• Automatic parameter validation and type conversion
• Rich documentation support through XML comments
• Near zero configuration required for basic usage

Prerequisites

• Any version of .NET that supports standard 2.0

Installation

dotnet add package MCPSharp

Quick Start

1. Define a Tool

Create a class and mark your method(s) with the [McpTool] attribute:

using MCPSharp;

public class Calculator
{
    [McpTool("add", "Adds two numbers")]  // Note: [McpFunction] is deprecated, use [McpTool] instead
    public static int Add([McpParameter(true)] int a, [McpParameter(true)] int b)
    {
        return a + b;
    }
}

2. Start the Server

await MCPServer.StartAsync("CalculatorServer", "1.0.0");

The StartAsync() method will automatically find any methods in the base assembly that are marked with the McpTool attribute. In order to add any methods that are in a referenced library, you can manually register them by calling MCPServer.Register<T>(); with T being the class containing the desired methods. If your methods are marked with Semantic Kernel attributes, this will work as well. If the client supports list changed notifications, it will be notified when additional tools are registered.

Advanced Usage

Dynamic Tool Registration

Register tools dynamically with custom implementation: