Agent skill · software engineering · github
dotnet-mcp-builder
Build Model Context Protocol (MCP) servers in C#/.NET against the current ModelContextProtocol 2.x NuGet packages. Helps with cases the model gets wrong without guidance — stale versions (0.x preview or 1.x-era defaults), the v2 stateless-by-default HTTP flip, the 2026-07-28 spec deprecations (roots/sampling/logging), MCP Apps and Tasks extension packages, elicitation URL mode, per-session HTTP wiring, OAuth and reverse-proxy deploy specifics, and debugging MapMcp / STDIO / Streamable-HTTP errors. Also covers STDIO and Streamable HTTP transports (SSE is deprecated), tools, prompts, resources, completions, and a basic .NET MCP client. Trigger when the user says or implies any .NET MCP server work: ModelContextProtocol, McpServerTool, MapMcp, WithStdioServerTransport, "MCP server in C#", "MCP tool in dotnet", "expose this as MCP", or names a primitive (prompt/resource/elicitation/MCP App) in a .NET context. Skip for MCP work in other languages.
Why this skill is useful
Provides specific guidance on building MCP servers with the latest .NET SDK, including niche commands and patterns not commonly known.
What it needs
Requires dotnet installed locally. About 4k tokens when loaded. Last updated 2026-08-07. 37,534 stars on the source repository.
What this skill does
Building MCP servers in .NET This skill helps you write production-quality MCP servers and basic clients in C#/.NET against the official ModelContextProtocol NuGet packages, maintained by Microsoft and the MCP project. It targets the stable 2.x line and the current spec (2026-07-28). When this skill earns its keep The .NET MCP SDK had years of preview packages (0.x-preview) before reaching 1.0, and v2 flipped several defaults. Without help, the model tends to: Pin a stale preview version that won't compile against current samples. Apply 1.x-era defaults that v2 reversed (HTTP was stateful by default; in 2.x Stateless defaults to true). Recommend capabilities the 2026-07-28 spec deprecates (roots, sampling, MCP-channel logging — now [Obsolete], warning MCP9005). Miss recent spec features (multi-round-trip inputrequired, discovery-first negotiation, MCP Apps/Tasks extension packages, elicitation URL mode, structured content blocks). Get HTTP transport details wrong (stateful/stateless, proxy buffering, OAuth wiring). Forget the STDIO stdout/stderr trap. If the task is one of those, load the matching reference and follow it. If it's truly trivial (e.g. "rename this tool method"), you don't need to read everything — the cardinal rules below are the minimum. Mental model in 30 seconds A .NET MCP server is an ordinary Microsoft.Extensions.Hosting (or WebApplication) app that wires an MCP server through DI: Primitives are plain C# methods on classes marked with attributes ([McpServerToolType] + [McpServerTool], [McpServerPromptType] + [McpServerPrompt], [McpServerResourceType] + [McpServerResource]). Parameters bind from JSON-RPC; the SDK builds the JSON Schema from the signature plus [Description] attributes. Server-to-client features (elicitation, progress notifications, and the now-deprecated sampling/roots/log notifications) are methods on the injected IMcpServer. …
How to use it
Reference it in AdaL, Claude Code, Cursor or any coding agent — nothing to install:
@skills github/dotnet-mcp-builder