C# SDK MCP — Cas d'usage, Installer & Démo en direct

Pourquoi l'utiliser

Fonctionnalités clés

First-party, co-maintained with Microsoft
Attribute-based tool registration — ASP.NET-style
Native DI, IHostedService, ILogger integration
Stdio + HTTP/SSE transports out of the box

Démo en direct

Aperçu en pratique

csharp-sdk.replay ▶ prêt

0/0

Installer

Choisissez votre client

~/Library/Application Support/Claude/claude_desktop_config.json · Windows: %APPDATA%\Claude\claude_desktop_config.json

{
  "mcpServers": {
    "csharp-sdk": {
      "command": "dotnet",
      "args": [
        "run",
        "--project",
        "./MyMcpServer"
      ]
    }
  }
}

Ouvrez Claude Desktop → Settings → Developer → Edit Config. Redémarrez après avoir enregistré.

~/.cursor/mcp.json · .cursor/mcp.json

{
  "mcpServers": {
    "csharp-sdk": {
      "command": "dotnet",
      "args": [
        "run",
        "--project",
        "./MyMcpServer"
      ]
    }
  }
}

Cursor utilise le même schéma mcpServers que Claude Desktop. La config projet l'emporte sur la globale.

VS Code → Cline → MCP Servers → Edit

{
  "mcpServers": {
    "csharp-sdk": {
      "command": "dotnet",
      "args": [
        "run",
        "--project",
        "./MyMcpServer"
      ]
    }
  }
}

Cliquez sur l'icône MCP Servers dans la barre latérale Cline, puis "Edit Configuration".

~/.codeium/windsurf/mcp_config.json

{
  "mcpServers": {
    "csharp-sdk": {
      "command": "dotnet",
      "args": [
        "run",
        "--project",
        "./MyMcpServer"
      ]
    }
  }
}

Même format que Claude Desktop. Redémarrez Windsurf pour appliquer.

~/.continue/config.json

{
  "mcpServers": [
    {
      "name": "csharp-sdk",
      "command": "dotnet",
      "args": [
        "run",
        "--project",
        "./MyMcpServer"
      ]
    }
  ]
}

Continue utilise un tableau d'objets serveur plutôt qu'une map.

~/.config/zed/settings.json

{
  "context_servers": {
    "csharp-sdk": {
      "command": {
        "path": "dotnet",
        "args": [
          "run",
          "--project",
          "./MyMcpServer"
        ]
      }
    }
  }
}

Ajoutez dans context_servers. Zed recharge à chaud à la sauvegarde.

claude mcp add csharp-sdk -- dotnet run --project ./MyMcpServer

Une seule ligne. Vérifiez avec claude mcp list. Supprimez avec claude mcp remove.

Cas d'usage

Usages concrets : C# SDK

Build an MCP server in .NET that exposes your existing services

👤 C#/.NET engineers with internal APIs ⏱ ~45 min intermediate

Quand l'utiliser : You're on .NET and want to expose business logic to agents without a rewrite.

Prérequis

.NET 8+ SDK — dotnet --version

Déroulement

Create the project

dotnet new console -n MyMcpServer. Add ModelContextProtocol NuGet. Use the minimal hosting template for MCP.✓ Copié

→ csproj + Program.cs with MCP hosted service
Add a tool

Create a static class with [McpServerToolType]. Add a method GetOrder(string id) decorated with [McpServerTool(Description="...")] that calls my existing OrderService via DI.✓ Copié

→ Tool compiles, description comes from attribute
Test with the inspector

Run the server as stdio. Launch the MCP Inspector via npx @modelcontextprotocol/inspector dotnet run. Call GetOrder.✓ Copié

→ Tool invocation returns order JSON

Résultat : A compiled, typed MCP server reusing your existing .NET services and DI container.

Pièges

Tool methods that are instance methods on a class need DI to work — Register the owning class in the ServiceCollection; the SDK resolves through DI
Async methods without proper cancellation tokens hang at shutdown — Accept CancellationToken ct as the last parameter on every tool — SDK injects it

Build a .NET console app that uses MCP servers

👤 C# devs building internal automation ⏱ ~30 min intermediate

Quand l'utiliser : You want deterministic .NET code (not an LLM loop) that calls MCP servers — e.g., a scheduled job that uses github + filesystem MCPs.

Déroulement

Add the client package

Create a console app. Reference ModelContextProtocol client. Add a config pointing at a stdio server (e.g. npx -y @modelcontextprotocol/server-github).✓ Copié

→ Client builds
Connect and call

Start the client, list tools, call list_repositories with my org name. Print the result.✓ Copié

→ Repos printed to console
Wrap as a scheduled job

Turn this into a Worker Service that runs nightly. Log metrics via ILogger.✓ Copié

→ Worker runs via dotnet run and schedules cleanly

Résultat : MCP as a library, not just a chat plugin — works inside any .NET process.

Pièges

Stdio servers take time to start, first call times out — Initialize the client at app startup and reuse; don't spawn per-call

Serve an MCP endpoint from an ASP.NET Core app

👤 .NET platform engineers ⏱ ~60 min advanced

Quand l'utiliser : You want the MCP server hosted inside an existing ASP.NET Core service, behind the same auth and ingress.

Prérequis

Existing ASP.NET Core app or willingness to start one — dotnet new web

Déroulement

Add MCP services + endpoint

In Program.cs, builder.Services.AddMcpServer().WithToolsFromAssembly(). Then app.MapMcp('/mcp').✓ Copié

→ /mcp endpoint responds to SSE handshake
Share auth with the rest of the app

Put the /mcp endpoint behind my existing JWT bearer auth middleware. Verify unauth'd requests get 401.✓ Copié

→ 401 unauth, 200 auth
Deploy and connect

Deploy. Wire a teammate's Claude Desktop via mcp-remote https://myapp.com/mcp with their JWT.✓ Copié

→ Team members see tools

Résultat : MCP alongside your existing API in one deploy with one auth story.

Pièges

Kestrel buffers SSE responses behind a reverse proxy — Disable response buffering; ensure IIS/nginx/Cloudflare in front also disable buffering for /mcp

Combiner avec : cloud-run

Combinaisons

Associez-le à d'autres MCPs pour un effet X10

csharp-sdk + cloud-run

Deploy .NET MCP server on Cloud Run alongside other microservices

Containerize my .NET MCP server (mcr.microsoft.com/dotnet/aspnet base), deploy to Cloud Run with a min-instance=1 for cold-start mitigation.✓ Copié

csharp-sdk + fastmcp

Comparison for polyglot shops — different SDKs, same protocol

Our team has both Python and .NET services. Use FastMCP for Python APIs and csharp-sdk for .NET APIs — both behind one ContextForge gateway.✓ Copié

Outils

Ce que ce MCP expose

Outil	Entrées	Quand appeler	Coût
[McpServerToolType]	attribute on a class	Mark classes whose methods should be exposed	free
[McpServerTool(Description)]	attribute on a method	Each method you want agents to call	free
AddMcpServer() / WithToolsFromAssembly()	fluent builder	Program.cs at startup	free
MapMcp('/path')	ASP.NET endpoint	ASP.NET hosting only	free
IMcpClient	stdio or SSE transport config	Client-side usage	free

Coût et limites

Coût d'exécution

Quota d'API: None — this is an SDK
Tokens par appel: No framework overhead beyond MCP protocol
Monétaire: Free, MIT licensed
Astuce: Use .NET's built-in logging and HealthChecks to catch problems before they balloon in prod

Sécurité

Permissions, secrets, portée

Stockage des identifiants : Standard .NET: user-secrets for dev, environment variables or Key Vault for prod

Sortie de données : Whatever your tools reach

Dépannage

Erreurs courantes et correctifs

Tool not appearing in inspector

WithToolsFromAssembly() only scans the executing assembly. For tools in referenced libraries, pass the Assembly explicitly: WithTools(typeof(MyTools).Assembly).

DI can't resolve my service in a tool method

Tool types must be registered in the container. Add builder.Services.AddScoped<OrderService>() before AddMcpServer.

ASP.NET MapMcp returns 404

You mapped after app.Run() — move MapMcp before Run. Also check the path doesn't conflict with other endpoints.

JSON serialization fails on enums

SDK uses System.Text.Json; add [JsonStringEnumConverter] on your enums or configure globally.

Alternatives

C# SDK vs autres

Alternative	Quand l'utiliser	Compromis
FastMCP (Python)	You're OK picking up Python — richer example ecosystem	Different language; team skill dependent
TypeScript MCP SDK	Node / TS shop	Similar DX, language choice

Plus

Ressources

📖 Lire le README officiel sur GitHub

🐙 Voir les issues ouvertes

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