windows-native-interop

---

name: windows-native-interop description: Design, implement, review, debug, and modernize Windows native interoperability for C#/.NET desktop applications. Use for Win32, HWND, HANDLE, COM, WinRT interop, CsWin32, P/Invoke, LibraryImport, GeneratedComInterface, callbacks, native DLLs, Windows SDK types, unmanaged memory, native resource ownership, error propagation, architecture-sensitive code, WinUI 3 interop, and low-level Windows API access. compatibility: Primarily C#/.NET desktop applications targeting Windows 10/11, including WinUI 3, WPF, WinForms, console applications, services, and class libraries. Verify minimum Windows version, target architecture, packaging model, and NativeAOT/trimming requirements before selecting an interop mechanism. metadata: domain: windows-native version: "1.0"

Windows Native Interop

Use this skill when managed Windows code must cross into Win32, COM, Windows Runtime interop, native DLLs, C ABI functions, native callbacks, Windows handles, HWND-based desktop APIs, or unmanaged memory.

Treat declarations and lifetime rules as part of the executable ABI contract.

Reference documents

This skill is split across modular reference files in resources/. Load only the document(s) relevant to the current task.

Reference	Contents	Load when
resources/overview.md	Goals; choosing the correct API layer; inspecting the project before changing interop.	Starting any interop work; orientation.
resources/declarations.md	CsWin32 and minimal NativeMethods.txt; LibraryImport; DllImport; WinRT is not Win32.	Selecting how to declare a native call.
resources/hwnd-winui.md	WinUI 3 HWND interop; owner-HWND WinRT UI; DPI-sensitive interop; window messages; subclassing.	HWND-based and WinUI 3 interop.
resources/types-and-handles.md	ABI-correct types; typed handles; SafeHandle; owned vs borrowed; invalid values; structures; generated types.	Handles, structures, and type mapping.
resources/strings-errors-com.md	Unicode strings; A/W variants; HRESULT vs Win32 errors; COM lifetime/apartments/identity.	Strings, error handling, COM.
resources/callbacks-memory-dlls.md	Native callbacks; calling conventions; unsafe code; pointer lifetimes; allocators; DLL loading/security.	Callbacks, memory, native DLLs.
resources/architecture-and-deployment.md	x64/ARM64/x86; AnyCPU; version gating; packaging; NativeAOT/trimming; abstraction layering; reentrancy; errors.	Architecture, deployment, layering.
resources/workflow-testing-review.md	Implementation workflow; testing; leak validation; anti-patterns; review checklist; source-of-truth; core principle.	Implementing, testing, and reviewing.

How to use

1. Read resources/overview.md for API-layer selection and the 10 goals.
2. Read the specific resources/*.md documents for the task (declarations, handles, strings/errors/COM, callbacks/memory/DLLs, architecture/deployment, etc.).
3. Apply the guidance to the host project, preserving its existing abstractions and conventions.