A UI designer agent produces design specifications, component definitions, and visual guidance that frontend developers can implement directly. In a fleet, it sits between the product requirements and the implementation: it translates feature descriptions into concrete UI decisions about spacing, typography, interaction states, and component composition.
A role-specific prompt should encode your design system: the token set, the component library, the grid, and the visual principles your product follows. Without this, a generalist agent produces designs that are internally consistent but incompatible with your existing UI.