What does usability primarily measure?

Usability primarily measures how easy a design's user interface is to use. This concept encompasses various aspects, such as the intuitiveness of the navigation, the efficiency with which users can accomplish tasks, and the overall user satisfaction. It evaluates how well a product supports its users in achieving their goals without unnecessary complications or frustrations.

In the context of user experience, usability plays a critical role, as it directly impacts how effectively and enjoyably users can interact with a product. A design that prioritizes usability ensures that users can understand the interface quickly, find what they need with minimal effort, and complete actions without confusion.

The other options focus on factors outside the core definition of usability. For example, while cost-effectiveness, visual appeal, and marketing success can influence a product's reception, they do not directly measure the ease of use that usability assesses. Thus, usability remains centered on the interaction between the user and the product's interface, making it an essential element of effective design.