The following are characteristics of maintainable code:

• No unused code (YAGNI).
• No duplicate code (DRY).
• Code is concise and short (KISS).
• Code is clear and easy to understand (KISS).
• Every function has a single purpose (the S in SOLID).
• Every module contains functions that relate to and work with each other (the S in SOLID).

Maintainability is an important aspect of any application. When designed properly, even large applications can be changed frequently and easily without fear. Applications can also last a long time, reducing the cost of the software.

Next, we will discuss software safety as another quality objective.