Microsoft published a plugin on May 13 that lets GitHub Copilot CLI and Claude Code drive the full WinUI 3 development cycle, from project scaffolding through signed MSIX packaging. The WinUI agent plugin ships one agent, eight skills, and several supporting tools targeting the loop developers run dozens of times a day: scaffold, build, run, test, iterate.
Native Windows app development with WinUI 3 pulls together several moving parts that rarely sit cleanly together for an AI agent. XAML and Fluent Design, MVVM patterns, code signing, and the Windows App SDK activation pipeline each have their own conventions, and agents running on generic web context have tended to mix WinUI 3 with older frameworks like UWP or stop short of actually running a built app to confirm it works.
How the plugin works
The central agent, called winui-dev, loads two skills by default: winui-dev-workflow, which handles project creation, building, and error diagnosis, and winui-design, which covers XAML layout, control selection, theming, and accessibility. Six additional skills cover code review, UI testing, MSIX packaging, WPF-to-WinUI migration, environment setup, and session diagnostics. The skills are designed to compose without interfering with each other.
A key design constraint was token cost. “Because each skill only loads what it needs and leans on the tools below for the rest, the agent does all of this in more than 70% fewer tokens than when we started – on the same model,” Nikola Metulev, Principal Software Engineer at Microsoft, explained.
The tools underneath
Three tools ship with the plugin. winui3-analyzer is a Roslyn analyzer distributed as a prebuilt DLL that the winui-dev-workflow skill automatically injects at build time to catch common WinUI 3 pitfalls such as UWP namespace leaks and missing EnsureCoreWebView2Async calls. winui-search is a native-AOT CLI that indexes WinUI Gallery and Community Toolkit samples so the agent can query real control patterns before writing XAML. winmd-cli provides offline API metadata lookup against .winmd and managed .dll files, letting the agent verify that an API exists with the expected signature before generating code.
The plugin also depends on the WinApp CLI, a separate command-line tool installable via winget, which handles packaged app installation, execution, signing, and UI automation. A temporary PowerShell wrapper called BuildAndRun.ps1 currently substitutes MSBuild for dotnet build when Visual Studio is present, working around a known XAML compiler issue that produces no diagnostic output on build failure. Microsoft states that wrapper will be removed once the platform fix ships in a future Windows App SDK release.
Status and access
The plugin is available now for GitHub Copilot CLI via the awesome-copilot registry. Microsoft is collecting feedback through the GitHub repository.
Download: Secure Foundations for AI Workloads on AWS
