Good Code Comments Should Explain Why, Not Just What the Code Does

A technical article published on DEV Community argues that code comments are most valuable when they explain the reasoning behind a decision, not merely restate what the code does. Repeating the logic already visible in the code adds noise and can become misleading if the implementation changes. The piece emphasizes that hidden constraints — such as external system behavior, compatibility requirements, or performance limits — are exactly what comments should document. Without such context, future engineers risk breaking functionality through changes that appear harmless on the surface. The article advises keeping reason-based comments concise, accurate, and updated whenever the underlying constraint changes.