Builds production-quality, accessible, responsive user-facing UIs. Use when building or modifying interfaces and pages, creating components, implementing layouts, meeting WCAG accessibility requirements, managing state, or when the output needs to look and feel production-quality rather than AI-gene

Frontend UI Engineering Overview Build production quality user interfaces that are accessible, performant, and visually polished. The goal is UI that looks like it was built by a design aware engineer at a top company — not like it was generated by an AI. This means real design system adherence, proper accessibility, thoughtful interaction patterns, and no generic "AI aesthetic." When to Use Building new UI components or pages Modifying existing user facing interfaces Implementing responsive layouts Adding interactivity or state management Fixing visual or UX issues Component Architecture File Structure Colocate everything related to a component: Component Patterns Prefer composition over configuration: Keep components focused: Separate data fetching from presentation: State Management Choose the simplest approach that works: Avoid prop drilling deeper than 3 levels. If you're passing props through components that don't use them, introduce context or restructure the component tree. Design System Adherence Avoid the AI Aesthetic AI generated UI has recognizable patterns. Avoid all of them: AI Default Why It Is a Problem Production Quality Purple/indigo everything Models default to visually "safe" palettes, making every app look identical Use the project's actual color palette Excessive gradients Gradients add visual noise and clash with most design systems Flat or subtle gradients matching the design system Rounded everything (rounded 2xl) Maximum rounding signals "friendly" but ignores the hierarchy of corner radii in real designs Consistent border radius from the design system Generic hero sections Template driven layout with no connection to the actual content or user need Content first layouts Lorem ipsum style copy Placeholder text hides layout problems that real content reveals (length, wrapping, overflow) Realistic placeholder content Oversized padding everywhere Equal generous padding destroys visual hierarchy and wastes screen space Consistent spacing scale Stock card grids Uniform grids are a layout shortcut that ignores information priority and scanning patterns Purpose driven layouts Shadow heavy design Layered shadows add depth that competes with content and slows rendering on low end devices Subtle or no shadows unless the design system specifies Spacing and Layout Use a consistent spacing scale. Don't invent values: Typography Respect the type hierarchy: Don't skip heading levels. Don't use heading styles for non heading content. Color Use semantic color tokens: text primary , bg surface , border default — not raw hex values Ensure sufficient contrast (4.5:1 for normal text, 3:1 for large text) Don't rely solely on color to convey information (use icons, text, or patterns too) Accessibility (WCAG 2.1 AA) Every component must meet these standards: Keyboard Navigation ARIA Labels Focus Management Meaningful Empty and Error States Responsive Design Design for mobile first, then expand: Test at these breakpoints: 320px, 768px, 1024px, 1440px. Loading and Transitions See Also For detailed accessibility requirements and testing tools, see ../../references/accessibility checklist.md . Common Rationalizations Rationalization Reality "Accessibility is a nice to have" It's a legal requirement in many jurisdictions and an engineering quality standard. "We'll make it responsive later" Retrofitting responsive design is 3x harder than building it from the start. "The design isn't final, so I'll skip styling" Use the design system defaults. Unstyled UI creates a broken first impression for reviewers. "This is just a prototype" Prototypes become production code. Build the foundation right. "The AI aesthetic is fine for now" It signals low quality. Use the project's actual design system from the start. Red Flags Components with more than 200 lines (split them) Inline styles or arbitrary pixel values Missing error states, loading states, or empty states No keyboard navigation testing Color as the sole indicator of state (red/green without text or icons) Generic "AI look" (purple gradients, oversized cards, stock layouts) Verification After building UI: [ ] Component renders without console errors [ ] All interactive elements are keyboard accessible (Tab through the page) [ ] Screen reader can convey the page's content and structure [ ] Responsive: works at 320px, 768px, 1024px, 1440px [ ] Loading, error, and empty states all handled [ ] Follows the project's design system (spacing, colors, typography) [ ] No accessibility warnings in dev tools or axe core

frontend-ui-engineering