What is a UI catalog?

A UI catalog is a visual collection of every user interface component used in a project.

It is needed for:

• Reviewing components. Buttons, forms, cards, tables, and more, all in one place.
• Reuse. Designers and developers see which elements already exist and don't reinvent them.
• Design unification. Every element follows a single system: the same spacing, colors, fonts, behavior.
• Documentation. A UI catalog often shows not just the visuals but a description too: how to use it, what states exist, what props are available.
• Testing. In a catalog, it's easier to find bugs, review edge states, and check accessibility.

Essentially, it is a showcase of every interface "building block". Storybook can play exactly this role.