Bottom-Up Design: The Best Way to Refactor Messed-Up Code Throughout my career in software development, I've encountered a recurring challenge: inheriting codebases that are messy, disorganized, and fragile. The common impulse in such situations is to suggest a full rewrite. While this might sound appealing at first, it is usually the wrong move. The smarter, more sustainable approach is to introduce design to the existing mess. Not by imposing a grand vision from above, but by letting the code itself guide you. This is what I call bottom-up design , and it is, in my opinion, the best way to refactor a problematic codebase. Why Rewriting Often Fails Rewriting an existing system from scratch is a massive undertaking. You lose all the small decisions and hidden logic that exist in the current system. Even worse, you now have to develop and maintain two systems in parallel: the old one that’s still in use, and the new one trying to catch up. As...