Comprehension Debt — When Your AI-Generated Codebase Outgrows Your Understanding

"I'm running a SaaS on code I don't fully understand." A founder told us this during our first call. Not ashamed. Just honest. The product had 80 paying users, revenue was growing, and the AI had built most of the codebase across 70+ sessions. But when a customer reported a billing error, nobody could trace where pricing logic actually lived. This post explains what comprehension debt is, how to measure it, and how to fix it structurally. What Is Comprehension Debt Comprehension debt is what happens when code is generated faster than it can be understood. AI produces working software. But "working" and "understood" are not the same thing. Each AI session solves the immediate task without asking whether the solution is structurally coherent with what came before. By month 4, the codebase has implicit conventions that nobody explicitly chose: Naming patterns that shifted mid-project Business logic in unexpected locations Functions that do three things Files that nobody can summarize in o