Rajeev Pentyala – Technical Blog on Power Platform, Azure and AI

The GitHub Copilot SDK is the agent that powers GitHub Copilot CLI, published as a library. Instead of chatting with Copilot, your application calls it from code.

In this post, lets use the SDK from a C# console app to repair a project that will not compile.

What is the GitHub Copilot SDK?

Copilot is usually something you talk to in an editor or a terminal. The SDK is the same agent, available as a library you call from code.

• It exposes the engine that runs the Copilot CLI. You call it from your own application.
• Copilot does the planning, picks the tools and edits the files. You do not write that loop.
• It runs wherever your code runs. Desktop tools, console apps, background jobs and web backends all work.
• The reply comes back as data. Your program can branch on it, log it, or fail a build with it.

Here is what the demo covers.

What This Does

• A small project named BrokenApp has a compile error placed in it on purpose.
• A second console app named CopilotRunner uses the Copilot SDK to repair it.
• The runner sends one plain English instruction. No file name and no line number.
• Copilot reads the file, edits it and rebuilds the project.
• The runner then checks the result itself and prints PASS or FAIL.

Prerequisites

Make sure you have the following ready.

• The .NET SDK. The sample here targets net10.0.
• The GitHub Copilot CLI. On Windows, install it with winget install GitHub.Copilot.
• Sign in once with copilot login. The SDK reuses that sign in, so your code needs no API key.
• A GitHub Copilot subscription. The free tier works, with limited usage.

Note: The SDK does not call an API directly. It talks to the Copilot CLI, so the CLI has to be installed. The CLI has no window of its own, so this also runs on a server or inside a container.

Lets start with the project that fails to build.

The Broken Project

• BrokenApp adds five numbers and prints the average. One line is wrong.
• Run dotnet build in that folder and it fails.

• The error reads CS0019: Operator '/' cannot be applied to operands of type 'int' and 'method group'.

Now lets build another console app which used ‘Copilot SDK’ and repairs the BrokenApp.

Copilot Runner App

• Create a new C# consoled App.
• Add the SDK package to the runner project.

dotnet add package GitHub.Copilot.SDK

• In the Program.cs, create a Client and a Session.

Three settings carry the work.

Notice there is no API key and no password in the code. The CLI already holds your sign in, and the SDK borrows it.

Important: PermissionHandler.ApproveAll approves every action without asking. Use it on a throwaway folder only.

• A Session is one conversation. Setting Model to auto lets Copilot pick a suitable model for you.

Send One Instruction

• The whole task goes in a single prompt.

• The prompt describes the goal. Copilot works out the steps. It also caps the work at three build attempts, so the run cannot continue forever.

Run It

• Run the runner project with dotnet run.

• The [tool] lines show what Copilot chose to do, one step at a time.
  • powershell ran the build and saw it fail.
  • view opened the file and read it.
  • apply_patch edited the wrong line.
  • powershell ran the build again to confirm.

Check the Result

Now that we ran the CopilotRunner app, the issue in BrokenApp should have fixed.

• Open the BrokenApp > Program.cs
• The issue got corrected. We can build the app with no errors.

If the Build Cannot Download the CLI

On a corporate network the build may fail with this error.

error MSB3923: Failed to download file
"https://registry.npmjs.org/@github/copilot-win32-x64/..."
The SSL connection could not be established.

• The package tries to fetch its own copy of the CLI while building, and the network blocks npm. Two settings avoid the download.
• In the .csproj, skip the download.

<CopilotSkipCliDownload>true</CopilotSkipCliDownload>

• In code, point at the CLI you already installed.

Connection = RuntimeConnection.ForStdio(cliPath),

Note: If npm is reachable, you do not need either setting. new CopilotClient() on its own uses the copy that ships with the package.

Summary

We took a project that would not compile, and repaired it from C# code using one instruction.

• Install the Copilot CLI and run copilot login once. The SDK reuses that sign in.
• Create a client, then a session, and set WorkingDirectory to limit where the agent can work.
• Describe the goal in the prompt. Leave out the file names and the steps.
• Verify the result in your own code, so the outcome is a value your program can use.

The full sample is on GitHub at RajeevPentyala/CopilotSDKDemo.

Official documentation: GitHub Copilot SDK and the .NET getting started guide

🙂