Fastify Best Practise

This is a comprehensive ruleset that teaches Claude how to write production-grade Fastify applications. It covers 14 topic areas from server setup and plugin architecture to authentication, error handling, and TypeScript integration. Each rule includes side-by-side bad/good examples so Claude can catch common mistakes like skipping schema validation or misusing encapsulation. The autoload-based project structure is solid and the testing guidance around inject() and buildServer factories is genuinely helpful. If you're building anything more serious than a hello-world API with Fastify, this will push Claude toward patterns that actually scale instead of the quick-and-dirty snippets you'd find in a basic tutorial.