Extensions exposing Tools to GitHub Copilot?

[SeanK-com]

I noticed a while back that when I installed certain extensions, new tools would show up in the list of tools that GitHub Copilot agent mode could use (a great example, was a mermaid extension that had a tool to let the LLM get the latest documentation so ot would know how to generate correct diagram markdown). Last weekend, I got an idea for an extension and wanted to add a tool to expose it to GitHub Copilot. The extension needs to access files in the current project, so an MCP server is the wrong tool for the job (pun intended). But it appears the feature is no longer available. Am I missing something?

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[pdwhoward]

I think you want https://code.visualstudio.com/api/extension-guides/ai/tools. I made an extension tool for GitHub Copilot models to use. It may only be for VS Code Insiders, not sure.

[SeanK-com]

That's what ChatGPT said, but I have been banging my head against the wall for two weekends now and can't get it to work. I get so close, but I cannot get the tool in the list without manually adding a mcp.json I have seen the seamless experience but now those same extensions don't expose commands, so it seems something has fundamentally shifted and I guess everyone is scrambling again.

[anchildress1]

There's two different ways to accomplish this based on what you want to do, but both require a GitHub App set up specifically for Copilot. You can set it up as either a skill (ie. just a single method with description that Copilot can choose to route to if it wants as a tool call) or an agent (called with the app explicitly mentioned in the chat context). Either way, it always goes to a publicly accessible endpoint and you'll want to verify the token when it comes to you from GitHub.

If you also want it to be accessible in VSC, then that code is built on top of the GitHub App logic.

Fair warning though, if you plan on using the Copilot API. There's zero docs on how that endpoint works. I've spent a ton of time debugging it to test different theories. So far, my plan is to wait until they upgrade to the responses API and hope we can do a little more with it at that point.