What I Learned Developing a Custom Framework *with* Generative AI

Introduction Since around the summer of 2025, I've been building a business application framework for Japan's SI industry as a personal project. From the very start, I fully adopted GitHub Copilot (generative AI) as a development partner. In this article, I'll share what I experienced while coding alongside generative AI — the fun moments, the frustrating ones, and the surprising discoveries. My development style: I write the code myself and have the AI review it. Rather than having AI generate everything, I use it as a reviewer for code I've already written. The Joy of Being Code-Reviewed After 20 Years For nearly 20 years, I've always been on the giving side of code reviews. I had no opportunity to have my own code reviewed. When you show your code to AI, it genuinely reviews it. And it lavishes you with praise . "This design is excellent," "This is enterprise-level" — being on the receiving end of a review after 20 years was a genuinely fun experience. My wife also chats with the AI