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Copilot SDK for .NET

Key Points

  • For Visual Studio (full IDE) Copilot integration: VSIX / Visual Studio SDK + Copilot APIs.
  • For VS Code Copilot extensions: JS/TS-based (Chat Extension Model).
  • Copilot Studio (low-code): build conversational copilots; integrates with M365.
  • GitHub Copilot Workspaces: cloud agent for tasks.

Visual Studio Copilot extensions

<Project Sdk="Microsoft.VisualStudio.Sdk">
  <ItemGroup>
    <PackageReference Include="Microsoft.VisualStudio.Sdk" />
    <PackageReference Include="Microsoft.VisualStudio.Copilot" />
  </ItemGroup>
</Project>

[Export(typeof(ICopilotChatExtension))]
public class MyProjectChatExtension : ICopilotChatExtension
{
    public string Id => "myproject";

    public async Task HandleAsync(ChatRequest request, IChatStream stream, CancellationToken ct)
    {
        if (request.Command == "review")
        {
            stream.Markdown("Reviewing your code...");
            // ...
        }
    }
}

(API surface varies by VS version; check current docs.)

Microsoft Copilot Studio

Low-code platform. Build copilots (formerly Power Virtual Agents) for: - M365 (Teams, Word, Outlook). - Customer-facing websites. - Internal apps.

Integrate with Power Platform (Power Automate flows, Dataverse, custom APIs).

For developers: extend with custom skills via Bot Framework or HTTP APIs.

[HttpPost("/api/copilot-skill")]
public async Task<IActionResult> Skill([FromBody] SkillRequest req)
{
    // Authenticated by Copilot Studio
    var resp = await ProcessAsync(req);
    return Ok(resp);
}

GitHub Copilot extensions (broader)

For agent/integration workloads:

GitHub.com → Copilot Workspaces → tasks autonomously completed → PR opened.

Extensions can listen to GitHub events; act in repos.

Use cases for .NET teams

  • Aspire copilot: scaffold AppHost integrations.
  • EF migrations copilot: generate migrations from DB diff.
  • Test generation copilot: from spec.
  • Security review copilot: against company policies.
  • Internal docs copilot: company knowledge base via RAG.

Architecture

[IDE Copilot] → [Your extension]
                  │
                  ├── Local context (open files, etc.)
                  ├── Backend service (Microsoft.Extensions.AI)
                  │      ├── Vector store (your docs)
                  │      ├── Custom tools
                  │      └── LLM (Azure OpenAI)
                  └── Return generated content

Extension is thin; backend has the AI logic.

Auth

  • VS extensions: VS auth context.
  • VS Code extensions: VS Code auth provider.
  • Copilot Studio: AAD / managed identity.

Distribution

  • Visual Studio Marketplace: VSIX.
  • VS Code Marketplace: VSIX (different format).
  • Private feeds: company-internal.

Roadmap

In 2026, Copilot tooling evolves quickly: - More agentic: autonomous task completion. - MCP integration in Copilot extensions. - Multi-IDE consistency.

Senior considerations

  • Local context only: don't transmit unnecessary code to LLM.
  • Auth tokens: rotate; secure storage.
  • Versioning: extensions break across IDE updates.
  • Test on multiple IDE versions.

Cross-references