C++ Core Guidelines by Stroustrup and Sutter for writing modern, safe, and efficient C++ code. Use when writing, reviewing, or refactoring C++ code to ensure type safety, resource safety, and performance. Triggers on C++ code tasks including interface design, resource management (memory, handles, locks), class design, error handling, concurrency, templates, and general code review. Use for questions like "review this C++ code", "how should I manage resources in C++", "best practices for C++ interfaces", or when writing any C++ code that should follow modern standards (C++11/14/17/20).