...Problems are arranged from warm-ups to brain-twisters, letting developers build intuition about distributive conditional types, inference in extends, variance, and other corner cases of the type system. The repository includes tests for each puzzle so you get immediate, compiler-driven feedback when your solution is correct. As a result, it doubles as both training material and a living reference for advanced patterns used in real libraries. Many engineers report that solving a handful of these dramatically improves their ability to write safe, expressive APIs with minimal runtime overhead.