C# MCP Server & Blazor WebAssembly Inspector

A companion repository for the blog post: Building a C# MCP Server with a Blazor WebAssembly Inspector.

This is a local, pedagogical MCP server built on .NET 10. It uses the official MCP C# SDK v2.2.0 and its stateless Streamable HTTP transport at POST /mcp, alongside a Blazor WebAssembly page for inspecting the sample tools. Customer and weather responses are simulated fixtures; the system-metrics tool intentionally reports live data from the local process. No tool queries an external system.

Protocol and transport

The server uses the current 2026-07-28 MCP HTTP wire format through MCP C# SDK v2.2.0. It is stateless: each POST /mcp request is independent, and the server does not issue or retain an Mcp-Session-Id. The current revision uses server/discover for bootstrap rather than the historical initialize handshake, and HTTP requests carry the protocol version in the MCP-Protocol-Version header.

Streamable HTTP is the recommended HTTP transport for new MCP servers. See the official MCP C# SDK transport guidance and stateless HTTP guidance for the protocol behaviour and production deployment options.

Related MCP server: Your Own MCP Server

Solution structure

• McpServerApp/McpServerApp: ASP.NET Core host for POST /mcp and the diagnostic inspector API.

• McpServerApp/McpServerApp.Client: Blazor WebAssembly diagnostic inspector UI.

• McpServerApp/McpServerApp.Tests: unit, integration, and bUnit component tests.

• e2e/: Playwright browser test for local diagnostic inspection and invocation.

Run locally

Prerequisites: .NET 10 SDK. Install Node.js only when running the browser test.

git clone https://github.com/cmalpass/csharp-mcp-server-blazor.git
cd csharp-mcp-server-blazor
dotnet run --project McpServerApp/McpServerApp

Open the local address printed by ASP.NET Core (normally http://localhost:5000) to explore the sample tools and local diagnostic log. For a client integration, point a current MCP client at the local POST /mcp endpoint and follow that client’s official, up-to-date configuration documentation.

Production considerations

This repository teaches the protocol and tool-inspection flow; it is not a complete production deployment template. Before exposing an MCP server, design authentication and authorization for the tool surface, validate allowed origins and host names, apply request/concurrency/rate limits, avoid logging secrets or raw untrusted payloads, and run behind HTTPS and an appropriate reverse proxy. The official C# SDK documentation is the source of truth for current transport and deployment behaviour.

If a reverse proxy terminates TLS, configure it to overwrite the forwarded headers and set Mcp:TrustedProxyAddress to that proxy's exact IP address (for example, Mcp__TrustedProxyAddress=10.0.0.10 as an environment variable). The application ignores forwarded headers unless this exact proxy is configured; never enable trust for arbitrary client-supplied X-Forwarded-* headers.

Testing

Run the .NET test suite:

dotnet test --solution McpServerApp/McpServerApp.sln --configuration Release

Run the local browser test:

npm ci
npm run test:e2e

Playwright keeps screenshots, traces, and its HTML report in ignored test-output directories (test-results/ and playwright-report/). Running the test never updates tracked documentation images.

License

This project is licensed under the MIT License.