Modifiability

Modifiability is the degree to which a product or system can be effectively and efficiently modified without introducing defects or degrading its existing quality. ISO/IEC 25010 classifies it as a sub-characteristic of maintainability, alongside modularity, reusability, analysability, and testability.

Where analysability asks how easily the impact of a change can be assessed, modifiability asks how cheaply the change can actually be made once it is understood. A system with low coupling and high cohesion tends to score well here, since a change to one part is less likely to ripple into others. A codebase choked with technical debt scores poorly, since even a small change risks unintended side effects.

Modifiability is closely related to, but distinct from, extensibility. Extensibility is specifically about adding new capability with minimal change to existing structure, whereas modifiability is the broader property of changing a system at all – including correcting or removing behavior – without breaking it.