What is Code Smell?

Code smells are not bugs — the code works correctly — but they indicate design weaknesses that may cause problems over time. Common smells include: Long Method (functions doing too much), God Class (a class that knows too much), Feature Envy (a method that uses another class's data more than its own), Primitive Obsession (using primitives instead of small objects), Shotgun Surgery (a change requires modifying many classes), and Duplicate Code. Martin Fowler's refactoring catalog provides specific techniques for addressing each smell. Static analysis tools (SonarQube, PHPStan) can detect certain code smells automatically.