McpSseServer 1.0.5

McpSseServer

A lightweight .NET library for building MCP (Model Context Protocol) servers with SSE (Server-Sent Events) transport in ASP.NET Core.

?? Features

• Minimal Setup - Get an MCP server running in just 8 lines of code
• Auto-Discovery - Classes marked with [McpHandler] are automatically registered
• Strongly-Typed - Write normal C# methods with typed parameters - no JSON parsing!
• SSE Transport - Full Server-Sent Events support with HTTP/1.1 compatibility
• Fallback Support - Automatic fallback to direct HTTP responses

?? Installation

dotnet add package McpSseServer

Or via Package Manager:

Install-Package McpSseServer

?? Quick Start

Step 1: Create a new ASP.NET Core Web API project

dotnet new web -n MyMcpServer
cd MyMcpServer
dotnet add package McpSseServer

Step 2: Configure Program.cs

using McpSseServer;

var builder = WebApplication.CreateBuilder(args);

builder.ConfigureKestrelForSse();
builder.Services.AddMcpSseServer(options =>
{
    options.ServerName = "My-MCP-Server";
    options.ServerVersion = "1.0.0";
});

var app = builder.Build();

app.UseMcpSseServer();  // Auto-discovers all [McpHandler] classes!

app.Run();

Step 3: Create your handlers

Create a new file Handlers/MyTools.cs:

using McpSseServer.Attributes;

namespace MyMcpServer.Handlers;

[McpHandler]
public class MyTools
{
    [McpTool("greet", "Greets a person by name")]
    public string Greet(string name)
    {
        return $"Hello, {name}!";
    }

    [McpTool("add", "Adds two numbers")]
    public string Add(double a, double b)
    {
        return $"Result: {a + b}";
    }
}

Step 4: Run and connect

dotnet run

Your MCP server is now running at http://localhost:5000/sse ??

?? Creating Tools

Tools are functions that the AI can call to perform actions.

Basic Tool

using McpSseServer.Attributes;

[McpHandler]
public class BasicTools
{
    [McpTool("generate_uuid", "Generates a new random UUID")]
    public string GenerateUuid()
    {
        return Guid.NewGuid().ToString();
    }
}

Tool with Parameters

[McpHandler]
public class MathTools
{
    [McpTool("calculate", "Performs arithmetic calculations")]
    public string Calculate(
        [McpParameter("Operation to perform", EnumValues = ["add", "subtract", "multiply", "divide"])] string operation,
        [McpParameter("First operand")] double a,
        [McpParameter("Second operand")] double b)
    {
        var result = operation switch
        {
            "add" => a + b,
            "subtract" => a - b,
            "multiply" => a * b,
            "divide" when b != 0 => a / b,
            "divide" => double.NaN,
            _ => throw new ArgumentException($"Unknown operation: {operation}")
        };

        return double.IsNaN(result) ? "Error: Division by zero" : $"{a} {operation} {b} = {result}";
    }
}

Tool with Optional Parameters

[McpHandler]
public class SearchTools
{
    [McpTool("search", "Searches for items")]
    public string Search(
        [McpParameter("Search query")] string query,
        [McpParameter("Maximum results")] int limit = 10,      // Optional with default
        [McpParameter("Sort order")] string? order = null)     // Nullable = optional
    {
        return $"Searching '{query}' with limit {limit}, order {order ?? "default"}";
    }
}

Parameter Type Mapping

?? Creating Resources

Resources provide read-only data that the AI can access.

using System.Text.Json;
using McpSseServer.Attributes;

[McpHandler]
public class MyResources
{
    [McpResource("config://app/settings", "App Settings", "Application configuration", "application/json")]
    public string GetAppSettings()
    {
        return JsonSerializer.Serialize(new
        {
            theme = "dark",
            language = "en",
            version = "1.0.0"
        });
    }

    [McpResource("docs://readme", "README", "Application documentation", "text/plain")]
    public string GetReadme()
    {
        return "# My Application\n\nWelcome to the documentation!";
    }

    [McpResource("info://server/status", "Server Status", "Current server status", "application/json")]
    public string GetServerStatus()
    {
        return JsonSerializer.Serialize(new
        {
            status = "running",
            timestamp = DateTime.UtcNow,
            uptime = TimeSpan.FromMinutes(42)
        });
    }
}

Resource Attribute Parameters

[McpResource(
    uri: "scheme://path/to/resource",  // Unique identifier
    name: "Display Name",               // Human-readable name
    description: "Description",         // What the resource contains
    mimeType: "application/json"        // Content type (default: text/plain)
)]

?? Creating Prompts

Prompts are reusable templates that help guide AI interactions.

using McpSseServer.Attributes;

[McpHandler]
public class MyPrompts
{
    [McpPrompt("greeting", "Generates a personalized greeting")]
    public string Greeting(
        [McpArgument("Name to greet")] string name,
        [McpArgument("Style: formal, casual, enthusiastic")] string style = "casual")
    {
        return style switch
        {
            "formal" => $"Dear {name}, I hope this message finds you well.",
            "enthusiastic" => $"Hey {name}! SO excited to chat with you!",
            _ => $"Hi {name}! How can I help you today?"
        };
    }

    [McpPrompt("code_review", "Creates a code review prompt")]
    public string CodeReview(
        [McpArgument("Programming language")] string language,
        [McpArgument("Focus area")] string focus = "general")
    {
        return $"Please review the following {language} code with focus on {focus}.";
    }

    [McpPrompt("summarize", "Creates a summarization prompt")]
    public string Summarize(
        [McpArgument("Summary length: brief, medium, detailed")] string length = "medium")
    {
        return length switch
        {
            "brief" => "Provide a 1-2 sentence summary.",
            "detailed" => "Provide a comprehensive summary with all key points.",
            _ => "Provide a balanced summary in 3-5 sentences."
        };
    }
}

?? Configuration Options

builder.Services.AddMcpSseServer(options =>
{
    // Server identity
    options.ServerName = "My-MCP-Server";
    options.ServerVersion = "1.0.0";
    
    // MCP protocol version
    options.ProtocolVersion = "2024-11-05";
    
    // Logging
    options.EnableLogging = true;      // Log MCP requests/responses
    options.EnableHttpLogging = true;  // Log HTTP requests
    
    // Endpoints (customize if needed)
    options.SseEndpoint = "/sse";           // SSE connection endpoint
    options.MessageEndpoint = "/message";   // Message endpoint
    
    // CORS configuration (opt-in)
    options.UseDefaultCors = true;          // Enable permissive CORS for browser clients
});

CORS Configuration

By default, CORS is not enabled. If you need your MCP server to be accessible from browser-based clients, you can enable the built-in permissive CORS policy:

builder.Services.AddMcpSseServer(options =>
{
    options.UseDefaultCors = true;  // Enables AllowAnyOrigin, AllowAnyMethod, AllowAnyHeader
});

Note: For production environments, consider configuring your own CORS policy instead of using the permissive default.

?? Attribute Reference

?? Connecting Clients

MCP Inspector

npx @anthropic/mcp-inspector http://localhost:5000/sse

Claude Desktop

Add to your Claude Desktop config (claude_desktop_config.json):

{
  "mcpServers": {
    "my-server": {
      "url": "http://localhost:5000/sse"
    }
  }
}

Custom Client

Connect to the SSE endpoint at /sse. The server will send an endpoint event with the message URL:

event: endpoint
data: http://localhost:5000/message?sessionId=<guid>

?? Example Project Structure

MyMcpServer/
??? Program.cs
??? Handlers/
?   ??? ToolHandlers.cs      # [McpHandler] with [McpTool] methods
?   ??? ResourceHandlers.cs  # [McpHandler] with [McpResource] methods
?   ??? PromptHandlers.cs    # [McpHandler] with [McpPrompt] methods
??? Properties/
?   ??? launchSettings.json
??? MyMcpServer.csproj

?? Complete Example

Program.cs

using McpSseServer;

var builder = WebApplication.CreateBuilder(args);

builder.ConfigureKestrelForSse();
builder.Services.AddMcpSseServer(options =>
{
    options.ServerName = "Demo-MCP-Server";
    options.ServerVersion = "1.0.0";
});

var app = builder.Build();
app.UseMcpSseServer();
app.Run();

Handlers/DemoHandlers.cs

using System.Text.Json;
using McpSseServer.Attributes;

namespace MyMcpServer.Handlers;

[McpHandler]
public class DemoHandlers
{
    // === TOOLS ===
    
    [McpTool("get_time", "Gets the current time")]
    public string GetTime(string timezone = "UTC")
    {
        var tz = TimeZoneInfo.FindSystemTimeZoneById(timezone);
        var time = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, tz);
        return $"Current time in {timezone}: {time:yyyy-MM-dd HH:mm:ss}";
    }

    [McpTool("calculate", "Basic calculator")]
    public string Calculate(string operation, double a, double b)
    {
        var result = operation switch
        {
            "add" => a + b,
            "subtract" => a - b,
            "multiply" => a * b,
            "divide" => a / b,
            _ => throw new ArgumentException($"Unknown: {operation}")
        };
        return $"{a} {operation} {b} = {result}";
    }

    // === RESOURCES ===
    
    [McpResource("info://status", "Status", "Server status", "application/json")]
    public string GetStatus()
    {
        return JsonSerializer.Serialize(new { status = "ok", time = DateTime.UtcNow });
    }

    // === PROMPTS ===
    
    [McpPrompt("hello", "Greeting prompt")]
    public string Hello(string name) => $"Hello {name}! How can I help?";
}

?? Source Code

GitHub Repository: https://github.com/keerukee/MCPServer_Sse.git

?? License

MIT License - feel free to use in your projects!

?? Recent Changes

Latest Update

• CORS Configuration (Opt-in): CORS is now optional and disabled by default. Use UseDefaultCors = true to enable a permissive CORS policy for browser-based clients. This gives you full control over CORS configuration in your application.

?? Contributing

Contributions are welcome! Please feel free to submit a Pull Request.