MCP Csharp

MCP C# Server Development

Overview

Build Model Context Protocol (MCP) servers using C# and .NET. This skill orchestrates your complete development workflow, from project creation to cloud deployment.

🎯 Quick Start

What do you need help with?

🚀 Complete Workflow

Phase 1: Create Your Server

When: Starting a new MCP server project

# Install the template (.NET 10+ required)
dotnet new install Microsoft.McpServer.ProjectTemplates

# Create stdio server (local/CLI)
dotnet new mcpserver -n MyMcpServer

# Or create HTTP server (remote/web)
dotnet new mcpserver -n MyMcpServer --transport http

Then: Add your tools using [McpServerToolType] and [McpServerTool] attributes.

📖 Full guide: Load mcp-csharp-create

Phase 2: Debug Your Server

When: Your server is created and you need to run/test it locally

Key steps:

1. Configure VS Code (.vscode/mcp.json) or Visual Studio
2. Run with dotnet run
3. Test with MCP Inspector or GitHub Copilot Agent Mode
4. Set breakpoints and debug

📖 Full guide: Load mcp-csharp-debug

Phase 3: Test Your Server

When: Your server works and needs automated tests

Key steps:

1. Create xUnit test project
2. Write unit tests for individual tools
3. Write integration tests with MCP client
4. Create evaluations to measure LLM effectiveness

📖 Full guide: Load mcp-csharp-test

Phase 4: Publish Your Server

When: Ready to distribute your server

📖 Full guide: Load mcp-csharp-publish

📋 Phase Detection

I'll help you figure out what phase you're in:

You're in Create phase if:

• You don't have a project yet
• You need to add new tools, prompts, or resources
• You're setting up transport (stdio or HTTP)

You're in Debug phase if:

• Your server won't start
• Tools aren't appearing in Copilot
• You need to step through code
• You're getting protocol errors

You're in Test phase if:

• Server works manually but needs automated tests
• You want to verify tool behavior
• You need to create LLM evaluations

You're in Publish phase if:

• Server is tested and ready for users
• You need to package for NuGet
• You need to containerize with Docker
• You want to deploy to Azure

🔧 Common Scenarios

Scenario: "I want to build an MCP server for [Service X]"

1. Load: mcp-csharp-create
2. Create project with dotnet new mcpserver -n ServiceXMcpServer
3. Study the Service X API documentation
4. Implement tools for key API operations
5. Test with MCP Inspector

Scenario: "My MCP server isn't working"

1. Load: mcp-csharp-debug
2. Check common issues:
   • stdio servers logging to stdout (should be stderr)
   • Missing [McpServerToolType] attribute
   • Tool not registered with .WithToolsFromAssembly()
3. Use MCP Inspector to test protocol
4. Set breakpoints and debug

Scenario: "I need to deploy my server to production"

1. Determine transport:
   • stdio → NuGet publishing
   • HTTP → Docker + Azure
2. Load: mcp-csharp-publish
3. Follow the publishing guide for your transport

📚 Reference

SDK Packages

Key Patterns

Tool Registration

[McpServerToolType]
public static class MyTools
{
    [McpServerTool, Description("Does something useful")]
    public static string DoSomething(
        [Description("Input parameter")] string input) =>
        $"Result: {input}";
}

Program.cs (stdio)

var builder = Host.CreateApplicationBuilder(args);
builder.Logging.AddConsole(o => o.LogToStandardErrorThreshold = LogLevel.Trace);
builder.Services.AddMcpServer()
    .WithStdioServerTransport()
    .WithToolsFromAssembly();
await builder.Build().RunAsync();

Program.cs (HTTP)

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddMcpServer()
    .WithHttpTransport()
    .WithToolsFromAssembly();
var app = builder.Build();
app.MapMcp();
app.Run();

🔗 Sub-Skills

Load these for detailed guidance on each phase:

📖 External Resources

• C# SDK: https://raw.githubusercontent.com/modelcontextprotocol/csharp-sdk/main/README.md
• Microsoft Template Guide: https://learn.microsoft.com/en-us/dotnet/ai/quickstarts/build-mcp-server
• MCP Specification: https://modelcontextprotocol.io/specification/