Type Design Performance

Here's a focused skill for writing performant .NET types, built by Aaron Stannard. It pushes you toward sealed classes, readonly structs for small immutable values, static pure functions, and deferred enumeration. The principles are opinionated but practical: seal unless you're designing for inheritance, return immutable collections at API boundaries, don't materialize enumerables until you need to. It's passed security audits from Gen Agent Trust Hub, Socket, and Snyk, and has picked up 314 installs with nearly 1,000 GitHub stars. If you're doing API design or code reviews in .NET and want to avoid common performance pitfalls, this gives you a solid checklist.