Legacy Code

Existing code in a system that is difficult to change safely, often because it lacks tests, uses outdated approaches, was written by people no longer available, or has accumulated technical debt over years of growth.

Legacy code slows product development and increases the risk of bugs when changes are made. Understanding it as a structural challenge rather than simply bad code allows founders to plan realistic remediation without halting product progress.

A founder acquires a competitor's product. The codebase is five years old with no automated tests and complex interdependencies her team does not fully understand. She allocates 20% of engineering capacity each sprint to writing tests and gradually refactoring the most risky sections before touching them for new features.