C# / .NET Samples

The C# samples use the ModelContextProtocol NuGet package and Microsoft.Extensions.Hosting to create MCP servers with minimal boilerplate.

Basic (stdio)
Advanced (HTTP + Azure)

Basic calculator server

The basic sample (03-GettingStarted/samples/csharp) is a stdio MCP server that exposes five calculator tools: Add, Subtract, Multiply, Divide, and IsPrime.

Clone and navigate

git clone https://github.com/microsoft/mcp-for-beginners.git
cd mcp-for-beginners/03-GettingStarted/samples/csharp

Review dependencies

The project file targets .NET 9 and references two packages:

calculator.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Hosting" Version="9.*" />
    <PackageReference Include="ModelContextProtocol" Version="0.*-*" />
  </ItemGroup>
</Project>

Run the server

dotnet run --project ./src/calculator.csproj

Server code

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

var builder = Host.CreateApplicationBuilder(args);
builder.Logging.AddConsole(consoleLogOptions =>
{
    // Configure all logs to go to stderr
    consoleLogOptions.LogToStandardErrorThreshold = LogLevel.Trace;
});
builder.Services
    .AddMcpServer()
    .WithStdioServerTransport()
    .WithToolsFromAssembly();
await builder.Build().RunAsync();

Tools are discovered automatically via WithToolsFromAssembly(). Any static method decorated with [McpServerTool] is registered as an MCP tool — no manual registration needed.

Configure in VS Code

Create .vscode/mcp.json in your workspace root:

.vscode/mcp.json

{
  "inputs": [
    {
      "type": "promptString",
      "id": "repository-root",
      "description": "Absolute path to the repository root"
    }
  ],
  "servers": {
    "calculator-mcp-dotnet": {
      "type": "stdio",
      "command": "dotnet",
      "args": [
        "run",
        "--project",
        "${input:repository-root}/03-GettingStarted/samples/csharp/src/calculator.csproj"
      ]
    }
  }
}

Run in Docker

Build and push a container image for the server:

# Build
docker build -t <YOUR-DOCKER-USERNAME>/mcp-calculator ./src

# Push
docker push <YOUR-DOCKER-USERNAME>/mcp-calculator

Then update mcp.json to run from the image:

.vscode/mcp.json

{
  "servers": {
    "mcp-calc": {
      "command": "docker",
      "args": ["run", "--rm", "-i", "<YOUR-DOCKER-USERNAME>/mcp-calculator"]
    }
  }
}

Advanced server with Streamable HTTP

The advanced sample (04-PracticalImplementation/samples/csharp) adds HTTP transport via ModelContextProtocol.AspNetCore, integrates .NET Aspire for local observability, and includes an azd configuration for one-command Azure deployment.

Navigate to the advanced sample

cd 04-PracticalImplementation/samples/csharp

Start with .NET Aspire

dotnet watch run --project ./src/AppHost

The Aspire dashboard opens in your browser. Note the http://localhost:XXXX/ URL shown for the calculator service.

Test with MCP Inspector

In a separate terminal:

npx @modelcontextprotocol/inspector http://localhost:5058

Select Streamable HTTP as the transport type, set the URL to http://localhost:5058/mcp, and click Connect.

Configure VS Code

.vscode/mcp.json

{
  "servers": {
    "calc-mcp": {
      "type": "http",
      "url": "http://localhost:5058/mcp"
    }
  }
}

Deploy to Azure

azd up

After deployment completes, update mcp.json with the Azure URL:

.vscode/mcp.json

{
  "servers": {
    "calc-mcp": {
      "type": "http",
      "url": "https://<your-app>.azurecontainerapps.io/mcp"
    }
  }
}

Available tools

Tool	Description
`Add`	Sum of two numbers
`Subtract`	Difference of two numbers
`Multiply`	Product of two numbers
`Divide`	Quotient with divide-by-zero guard
`IsPrime`	Primality check
`NextFivePrimeNumbers`	Next five primes after a given number

Try it with GitHub Copilot Chat

With the server running and mcp.json configured, try these prompts in VS Code Copilot Chat:

"3 prime numbers after 6780"
"John has 24 lollies and wants to share them equally with 3 kids. How many each?"

Basic Examples

Basic calculator server

Server code

Configure in VS Code

Run in Docker

Advanced server with Streamable HTTP

Available tools

Try it with GitHub Copilot Chat

Build docs developers (and LLMs) love

Basic Examples

Documentation Index

​Basic calculator server

​Server code

​Configure in VS Code

​Run in Docker

​Advanced server with Streamable HTTP

​Available tools

​Try it with GitHub Copilot Chat

Build docs developers (and LLMs) love

Basic calculator server

Server code

Configure in VS Code

Run in Docker

Advanced server with Streamable HTTP

Available tools

Try it with GitHub Copilot Chat