Build Model Context Protocol (MCP) servers and clients in .NET with MCPSharp.
Create MCP-compliant tools and functions that AI models can discover and use.
Features easy to use attribute-based API allowing anyone to spin up a server in minutes,
and a Microsoft.Extensions.AI compatible client that generates AIFunctions,
ready to be consumed by any IChatClient or compatible system.
await MCPServer.StartAsync("EchoServer", "1.0.0");
--- server:
class MyTool
{
[McpTool("echo","returns the input string back to you")]
public string echo(string input) => input;
}
---client:
var client = new MCPClient("MyClient","1.0.0", "EchoServer.exe" //or dotnet EchoServer.dll if you wish
await client.CallToolAsync("echo", new Dictionary<string, object>{{"input", "input string to echo"}});
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
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;
}
}
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:
MCPServer.AddToolHandler(new Tool()
{
Name = "dynamicTool",
Description = "A dynamic tool",
InputSchema = new InputSchema {
Type = "object",
Required = ["input"],
Properties = new Dictionary<string, ParameterSchema>{
{"input", new ParameterSchema{Type="string", Description="Input value"}}
}
}
}, (string input) => { return $"You provided: {input}"; });
Resources API
Define and expose resources:
[McpResource("settings", "resource://settings", "application/json", "Application settings")]
public string Settings { get; set; } = "{ \"theme\": \"dark\" }";
// Or as a method
[McpResource("user", "resource://{name}", "text/plain", "User information")]
public string GetUser(string name) => $"Information about {name}";
This list can be plugged into the ChatOptions.Tools property for an IChatClient, Allowing MCP servers to be used seamlessly with Any IChatClient Implementation.
Semantic Kernel Integration
using Microsoft.SemanticKernel;
public class MySkillClass
{
[KernelFunction("MyFunction")]
[Description("Description of my function")]
public string MyFunction(string input) => $"Processed: {input}";
}
// Register with MCPServer
MCPServer.Register<MySkillClass>();
Currently, This is the only way to make a Semantic kernel method registerable with the MCP server. If you have a use case that is not covered here, please reach out!
API Reference
Attributes
[McpTool] - Marks a class or method as an MCP tool
Optional parameters:
Name - The tool name (default: class/method name)
Description - Description of the tool
[McpParameter] - Provides metadata for function parameters
Optional parameters:
Description - Parameter description
Required - Whether the parameter is required (default: false)
[McpResource] - Marks a property or method as an MCP resource
Parameters:
Name - Resource name
Uri - Resource URI (can include templates)
MimeType - MIME type of the resource
Description - Resource description
Server Methods
MCPServer.StartAsync(string serverName, string version) - Starts the MCP server
MCPServer.Register<T>() - Registers a class containing tools or resources
MCPServer.AddToolHandler(Tool tool, Delegate func) - Registers a dynamic tool
client.CallToolAsync(string name, Dictionary<string, object> parameters) - Call a tool
client.GetResourcesAsync() - Get available resources
client.GetFunctionsAsync() - Get tools as AIFunctions
XML Documentation Support
MCPSharp automatically extracts documentation from XML comments:
/// <summary>
/// Provides mathematical operations
/// </summary>
public class Calculator
{
/// <summary>
/// Adds two numbers together
/// </summary>
/// <param name="a">The first number to add</param>
/// <param name="b">The second number to add</param>
/// <returns>The sum of the two numbers</returns>
[McpTool]
public static int Add(
[McpParameter(true)] int a,
[McpParameter(true)] int b)
{
return a + b;
}
}
This allows you to be able to quickly change the names and descriptions of your MCP tools without having to recompile. For example, if you find the model is having trouble understanding how to use it correctly.
Migration Notes
[McpFunction] is deprecated and replaced with [McpTool] for better alignment with MCP standards
Use MCPServer.Register<T>() instead of MCPServer.RegisterTool<T>() for consistency (old method still works but is deprecated)
Contributing
We welcome contributions! Please feel free to submit a Pull Request.
