Code Smell Detector

A code smell is a surface indicator in source code that usually corresponds to a deeper problem. The term was popularized by Martin Fowler in 'Refactoring'. Smells don't indicate bugs — code with smells can work correctly — but they signal areas where the code will be harder to maintain, extend, or test. Common smells: long methods, magic numbers, deep nesting, duplicated code, god classes.

A magic number is a numeric literal used directly in code without explanation: if (retries > 3) or timeout = 30000. They're problems because the intent is unclear (why 3? why 30000?), they're hard to update consistently, and they make code impossible to read without context. Fix: extract to named constants: const MAX_RETRIES = 3 or const TIMEOUT_MS = 30_000.

A god class (or god object) is a class that knows too much or does too much — it has too many responsibilities, too many methods, and too many dependencies. Signs: classes longer than 300 lines, more than 10 public methods, more than 7 fields. God classes violate the Single Responsibility Principle and become bottlenecks where every change risks breaking unrelated functionality.

Not all smells need immediate refactoring. Prioritize by: (1) smells in code you're actively changing ('the boy scout rule'), (2) smells causing bugs or making tests impossible, (3) smells in hot paths that slow development velocity. Never refactor just for cleanliness in stable, untouched code — the risk of introducing bugs outweighs the benefit.

DRY (Don't Repeat Yourself) states that every piece of knowledge should have a single, unambiguous representation in a system. Duplicated code violates DRY — when logic changes, you must find and update every copy. Fix by extracting shared logic into functions or modules. Caveat: not all similar code should be merged; sometimes duplication is accidental, not structural, and merging it creates harmful coupling.