Comments are often not a smell at all - they can be very helpful. Particularly if they explain why a piece of code is written like it is. However, sometimes people write comments instead of taking the time to make the actual code readable and self-explanatory. If you need a comment, it could be a sign you have a primitive obsession instead of using domain classes, or could do with better names for your classes and functions. Some comments would be better off as assert statements documenting your assumptions.

All Code Smells