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 - 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
Expose your .NET methods as MCP endpoints with simple attributes
Generate accurate MCP schema documentation automatically
Handle MCP protocol details and JSON-RPC communication seamlessly
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
Features
Easy-to-use attribute-based API ([McpTool], [McpFunction])
Built-in JSON-RPC support with automatic request/response handling
Automatic parameter validation and type conversion
Create a class and mark it with the [McpTool] attribute:
using MCPSharp;
[McpTool]
public class Calculator
{
[McpFunction]
public static int Add([McpParameter(true)] int a, [McpParameter(true)] int b)
{
return a + b;
}
}
Description - A description of the tool. This should be used to provide additional
context to the tool. Will use the XML summary (see relevant section) if not provided.)
[McpFunction] - Marks a method as an MCP function
Optional parameters:
Name - The function name (default: method name)
Description - A description of the function. This should be used to provide additional
context to the function. Will use the XML summary (see relevant section) if not provided.)
[McpParameter] - Provides metadata for function parameters
Optional parameters:
Description - A description of the parameter. This should be used to provide additional
context to the parameter.
Required - Whether the parameter is required (default: false)
Additional Methods
MCPServer.StartAsync(string toolName, string toolVersion) - Starts the MCP server with the specified
tool name and version. This method should be called to start the server.
MCPServer.RegisterTool<T>() - Registers a tool with the server. This method should be called before
starting the server, IF you wish to register a tool that is loaded from an external class library,
or a semantic kernel function.
Any [McpTool] that are part of the main assembly will be automatically registered.
There is a client class included as well, designed to help with testing. It is provided as is, and is
not extremely flexible. I would suggest anyone wanting a client to check out
mcpdotnet, as it seems to be much more feature complete. If you
would like to use the MCPSharp implementation anyway, check out the MCPSharp.Test project for how it works.
Example
Here's a complete example:
using MCPSharp;
MCPServer.StartAsync("StringTools", "1.0.0");
[McpTool("string_tools", "String manipulation utilities")]
public class StringTools
{
[McpFunction("concat", "Concatenates two strings with separator")]
public static string Concat(
[McpParameter(true)] string first,
[McpParameter(true)] string second,
[McpParameter(Description = "Separator between strings")] string separator = " "
)
{
return $"{first}{separator}{second}";
}
}
XML Documentation Support
MCPSharp can automatically extract documentation from XML comments to provide rich descriptions for your tools and functions in the MCP schema.
Enable XML Documentation
In your project file (.csproj), add or modify the following settings:
Use standard XML documentation comments on your tools and functions:
/// <summary>
/// Provides mathematical operations
/// </summary>
[McpTool("calculator")]
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>
[McpFunction]
public static int Add(
[McpParameter(true)] int a,
[McpParameter(true)] int b)
{
return a + b;
}
}
Documentation Priority
MCPSharp uses the following priority order when determining descriptions:
Explicit descriptions in attributes ([McpTool(Description = "...")])
XML documentation comments (if the XML documentation file is present)
Roadmap
We have several features planned for future releases of MCPSharp:
Complex Object Parameter Parsing: Properly parse input/return parameters that are complicated objects. Currently they can be used, but the library will not expose the shape of the object to the client, so it must be mentioned in the description somewhere.
Tool Change Notifications: Implement notifications for tool changes (updates client when tools are added/updated/deleted)
Standardized Error Handling: Standardize error handling across the library.
Additional Endpoints: Implement the rest of the endpoints like resources, etc.
SSE Transport: enable the use of Server-Sent Events as a transport mechanism.
IntelliSense Support
The XML documentation also provides IntelliSense support in IDEs when consuming your MCP tools as a library.
Contributing
We welcome contributions! Please feel free to submit a Pull Request.