Add .NET MCP Server authoring skill by Copilot · Pull Request #33 · dotnet/skills

Copilot · 2026-02-17T16:51:16Z

Developers building MCP (Model Context Protocol) servers for AI agents lack reliable guidance on transport selection, hosting patterns, and SDK usage for the evolving .NET MCP ecosystem.

Changes

New skill: skills/dotnet-mcp-server/SKILL.md (473 lines) with references/code-examples.md for detailed examples
Transport decision tree: stdio for local CLI tools vs HTTP/SSE for shared services with auth/CORS
Framework guidance: .NET 10 LTS recommended (current as of Feb 2026), with .NET 9 STS and .NET 8 LTS tradeoffs
Scaffolding templates: Console host with ModelContextProtocol for stdio (with stderr logging), ASP.NET Core with ModelContextProtocol.AspNetCore for HTTP
Tool/resource patterns: IMcpTool and IMcpResource implementations with attribute-based method registration
HTTP concerns: Authentication middleware, CORS policies, endpoint routing
Testing strategy: Unit test tools in isolation, integration test via host instantiation, manual test with JSON-RPC over stdin/HTTP
Packaging and deployment: Standalone executables, Native AOT, container deployment with Docker, and deployment considerations

Example

public class CalculatorTool : IMcpTool
{
    [McpToolMethod("add")]
    [Description("Adds two numbers together")]
    public Task<int> AddAsync(
        [Description("First number")] int a,
        [Description("Second number")] int b)
    {
        return Task.FromResult(a + b);
    }
}

Targets Copilot CLI, VS Code, Claude Desktop, and web-based agent consumers.

Key Technical Details

stdio logging: Configured to use stderr exclusively (LogToStandardErrorThreshold) to maintain MCP protocol compliance
File organization: Main skill under 500 lines with detailed examples in references/ directory per repository conventions

Original prompt

This section details on the original issue you should resolve

<issue_title>Skill: .NET MCP Server Authoring</issue_title>
<issue_description>## Problem

AI agents are increasingly powered by MCP (Model Context Protocol) servers, and .NET is a natural fit for building them. However, developers face a maze of decisions: stdio vs HTTP transport, which target framework to use, how to structure tools and resources, and how to handle authentication for HTTP endpoints. Generic AI guidance is unreliable here — it mixes up transport semantics, suggests incorrect hosting patterns, and doesn't know the current state of the .NET MCP SDK.

What expert .NET knowledge would this encode?

Transport selection guidance: When to use stdio (local tools, CLI agents, Copilot CLI) vs HTTP/SSE (shared services, multi-client, cloud-hosted) — with decision tree

Target framework selection: .NET 8 LTS vs .NET 9 vs .NET 10 tradeoffs for MCP servers specifically (hosting model differences, AOT compatibility, support lifecycle)

Project scaffolding: Correct package references (ModelContextProtocol, Microsoft.Extensions.Hosting), minimal hosting setup for each transport

Tool and resource authoring: Proper patterns for defining tools, resources, and prompts using the .NET MCP SDK attributes and conventions

HTTP-specific concerns: Authentication, CORS, endpoint routing, and deployment considerations

Testing patterns: How to test MCP tools in isolation and integration-test a running server

Skill concept

A guided skill that walks the developer through building a .NET MCP server from scratch. It should:

Ask the right questions first — What will consume this server? (Copilot CLI, VS Code, Claude Desktop, a web app?) How many concurrent clients? Does it need auth?

Guide transport selection — Based on answers, recommend stdio or HTTP (or both via dual hosting)

Guide target framework selection — Based on deployment target, AOT needs, and support requirements

Scaffold the project — Generate the correct project file, hosting setup, and initial tool/resource structure

Validate the result — Ensure the server starts, responds to initialize, and tools are discoverable

Why customers would value this

MCP is the emerging standard for agent extensibility. Developers who want to build tools for Copilot, Claude, or other AI agents need to stand up MCP servers — and .NET developers deserve first-class guidance for doing it idiomatically. The .NET MCP SDK is new and fast-moving; the team knows the correct patterns before they're widely documented.

Scope

stdio and HTTP transports

Target framework decision guidance

Basic tool and resource authoring

Does NOT cover: custom transport implementations, MCP client authoring, or proxy/gateway patterns</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes Skill: .NET MCP Server Authoring #30

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

Co-authored-by: artl93 <9855795+artl93@users.noreply.github.com>

artl93 · 2026-02-17T17:34:58Z

+
+var builder = Host.CreateApplicationBuilder(args);
+
+builder.Logging.AddConsole();


@copilot - why are we logging to console? Would it be better to log to file pr better to stderr per spec? Spewing to the console creates problems and is non-compliant for stdio servers

Fixed in 94e9a59. Logging now configured to write to stderr using LogToStandardErrorThreshold = LogLevel.Trace, keeping stdout clear for JSON-RPC messages per MCP stdio transport spec.

artl93 · 2026-02-17T17:36:51Z

+  }
+}
+```
+


@copilot - should we add a step for packaging / deployment?

Added in 94e9a59 as Step 8. Covers standalone executables, Native AOT, container deployment with Docker, and deployment considerations. Detailed examples moved to references/code-examples.md.

artl93 · 2026-02-17T17:38:01Z

+  - Consider if project timeline aligns with .NET 10 release
+  - Use preview versions only for experimentation
+
+**Decision tree**: Use .NET 8 LTS unless the user has a specific reason to use .NET 9 features or is targeting .NET 10 for long-term projects starting after its release.


@copilot - please prefer .NET 10 - today is Feb 17, 2026, so the information here is quite dated.

Updated in 94e9a59. Now recommends .NET 10 LTS as current best choice (support through Nov 2027), with .NET 9 STS approaching end of support (May 2026) and .NET 8 LTS as fallback for compatibility constraints.

…d deployment step Co-authored-by: artl93 <9855795+artl93@users.noreply.github.com>

leslierichardson95 · 2026-02-19T18:58:19Z

@artl93 I think this skill looks good. Maybe there's also an opportunity to merge its content with some of the skills I recently created a PR for? #36

artl93 · 2026-02-19T19:05:22Z

@leslierichardson95 - yours to my eyes (without testing) yours looks more comprehensive. Are you opposed to going with yours? What do you think yours could use?

leslierichardson95 · 2026-02-19T19:33:47Z

@leslierichardson95 - yours to my eyes (without testing) yours looks more comprehensive. Are you opposed to going with yours? What do you think yours could use?

@artl93 I'm not opposed to going with mine. At a glance, I think mine could also definitely use some of your content like the following:

the docker-compose.yml file example
the input specification chart for extra clarity / description
the common pitfalls chart
additional resources section
Authentication details / examples

artl93 · 2026-02-19T20:45:55Z

Have copilot just grab ‘em (local CLI / VSCode / VS should work great for looking at two PRs and updating an existing one). I’m just on calls the rest of the day. :-( From: leslierichardson95 ***@***.***> Date: Thursday, February 19, 2026 at 11:34 AM To: dotnet/skills ***@***.***> Cc: Art Leonard ***@***.***>, Mention ***@***.***> Subject: Re: [dotnet/skills] Add .NET MCP Server authoring skill (PR #33) [https://avatars.githubusercontent.com/u/7150306?s=20&v=4]leslierichardson95 left a comment (dotnet/skills#33)<#33 (comment)> @leslierichardson95<https://github.com/leslierichardson95> - yours to my eyes (without testing) yours looks more comprehensive. Are you opposed to going with yours? What do you think yours could use? @artl93<https://github.com/artl93> I'm not opposed to going with mine. At a glance, I think mine could also definitely use some of your content like the following: * the docker-compose.yml file example * the input specification chart for extra clarity / description * the common pitfalls chart * additional resources section * Authentication details / examples — Reply to this email directly, view it on GitHub<#33 (comment)>, or unsubscribe<https://github.com/notifications/unsubscribe-auth/ACLGGM5UAU4C7MXY43IMFI34MYF3FAVCNFSM6AAAAACVNXWMN6VHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTSMRZGQ3TONBTGU>. You are receiving this because you were mentioned.

leslierichardson95 · 2026-02-19T23:01:01Z

Have copilot just grab ‘em (local CLI / VSCode / VS should work great for looking at two PRs and updating an existing one). I’m just on calls the rest of the day.

@artl93 I just updated my PR with some of the content I mentioned above if you wanna take a look :)
#36

timheuer · 2026-02-20T01:01:12Z

yes let's get one simplified MCP authoring skill between this and #36 please

artl93 · 2026-02-20T01:05:04Z

Let's take Leslie's.

Initial plan

6b3aa94

Copilot AI assigned Copilot and artl93 Feb 17, 2026

Copilot started work on behalf of artl93 February 17, 2026 16:51 View session

Add dotnet-mcp-server skill with comprehensive MCP authoring guidance

40fef99

Co-authored-by: artl93 <9855795+artl93@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add expert guidance for .NET MCP server authoring~~ Add .NET MCP Server authoring skill Feb 17, 2026

Copilot AI requested a review from artl93 February 17, 2026 16:58

Copilot finished work on behalf of artl93 February 17, 2026 16:58

artl93 assigned leslierichardson95 and jeffhandley Feb 17, 2026

artl93 requested changes Feb 17, 2026

View reviewed changes

artl93 marked this pull request as ready for review February 17, 2026 17:39

Copilot started work on behalf of artl93 February 17, 2026 17:39 View session

artl93 unassigned jeffhandley and leslierichardson95 Feb 17, 2026

artl93 requested review from jeffhandley and leslierichardson95 February 17, 2026 17:40

Address PR feedback: update framework guidance, fix stdio logging, ad…

94e9a59

…d deployment step Co-authored-by: artl93 <9855795+artl93@users.noreply.github.com>

Copilot AI requested a review from artl93 February 17, 2026 17:43

Copilot finished work on behalf of artl93 February 17, 2026 17:43

artl93 closed this Feb 20, 2026

ViktorHofer deleted the copilot/add-dotnet-mcp-guidance branch March 4, 2026 12:20


		var builder = Host.CreateApplicationBuilder(args);

		builder.Logging.AddConsole();

Conversation

Copilot AI commented Feb 17, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Changes

Example

Key Technical Details

What expert .NET knowledge would this encode?

Skill concept

Why customers would value this

Scope

Comments on the Issue (you are @copilot in this section)

Uh oh!

artl93 Feb 17, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 17, 2026

Choose a reason for hiding this comment

Uh oh!

artl93 Feb 17, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 17, 2026

Choose a reason for hiding this comment

Uh oh!

artl93 Feb 17, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI Feb 17, 2026

Choose a reason for hiding this comment

Uh oh!

leslierichardson95 commented Feb 19, 2026

Uh oh!

artl93 commented Feb 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

leslierichardson95 commented Feb 19, 2026

Uh oh!

artl93 commented Feb 19, 2026 via email

Uh oh!

leslierichardson95 commented Feb 19, 2026

Uh oh!

timheuer commented Feb 20, 2026

Uh oh!

artl93 commented Feb 20, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

Copilot AI commented Feb 17, 2026 •

edited

Loading

artl93 commented Feb 19, 2026 •

edited

Loading