frontend-ui-engineering

Cómo usar

Copia el comando y revisa el paquete antes de instalarlo en tu entorno de agente.
Consulta las herramientas, credenciales y entornos necesarios en el documento original.
Describe las entradas y el resultado deseado; contrasta la salida con las fuentes.

npx skills add https://github.com/jpeetz/agent-skills --skill frontend-ui-engineering

Antes de empezar

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Documento original del Skill

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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:

src/components/
  TaskList/
    TaskList.tsx         # Component implementation
    TaskList.test.tsx    # Tests
    types.ts             # Component-specific types (if needed)

Component Patterns

Prefer composition over configuration:

tsx

// Good: Composable
<Tasks>
  <TaskItem task={task} onToggle={handleToggle} onDelete={handleDelete} />
</Tasks>

// Avoid: Over-configured
<SuperTaskPanel mode="edit" enableDrag={true} showCompleted={false} ... />

Separate data fetching from presentation:

tsx

// Container: handles data
export function TaskListContainer() {
  const { tasks, isLoading, error } = useTasks();
  if (isLoading) return <LoadingSkeleton />;
  if (error) return <ErrorState message={error} />;
  if (tasks.length === 0) return <EmptyState />;
  return <TaskList tasks={tasks} />;
}

// Presentation: handles rendering
export function TaskList({ tasks }: { tasks: Task[] }) {
  return <div>{tasks.map(task => <TaskItem key={task.id} task={task} />)}</div>;
}

State Management

Choose the simplest approach that works:

Local state (useState)        → Component-specific UI state
Lifted state                  → Shared between 2-3 sibling components
Context                       → Theme, auth, locale (read-heavy, write-rare)
URL state (searchParams)      → Filters, pagination, shareable UI state
Server state (React Query)    → Remote data with caching
Global store (Zustand, Redux) → Complex client state shared app-wide

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

Reference-led UI Quality

When the product needs a distinct visual direction:

Collect evidence before choosing a layout
Study 2-3 relevant screens. Record decisions about hierarchy, density, navigation, controls, responsive behavior, and interaction states
Turn those decisions into a short design contract before implementation
Rebuild using the product's own components, tokens, content, and visual language
Never copy another product's branding, proprietary text, or exact layout

Avoid the AI Aesthetic

AI Default	Why It Is a Problem	Production Quality
Purple/indigo color schemes	Models default to visually "safe" palettes	Use the project's actual color palette
Excessive gradients	Add visual noise, clash with design systems	Flat or subtle gradients from the design system
Maximum border-radius everywhere	Ignores the hierarchy of corner radii in real designs	Consistent border-radius from the design system
Generic hero sections	Template-driven, no connection to real content	Content-first layouts
Lorem ipsum-style copy	Hides layout problems that real content reveals	Realistic placeholder content
Oversized padding	Destroys visual hierarchy, wastes screen space	Consistent spacing scale
Stock card grids	Ignores information priority and scanning patterns	Purpose-driven layouts
Shadow-heavy design	Competes with content, slows rendering on low-end devices	Subtle or no shadows unless specified

Spacing and Layout

Use a consistent spacing scale. Don't invent values:

css

/* Use the scale: 0.25rem increments (or whatever the project uses) */
/* Good */ padding: 1rem;  /* 16px */
/* Good */ gap: 0.75rem;   /* 12px */
/* Bad */  padding: 13px;  /* Not on any scale */
/* Bad */  margin-top: 2.3rem; /* Not on any scale */

Typography

Respect the type hierarchy:

h1 → Page title (one per page)
h2 → Section title
h3 → Subsection title
body → Default text
small → Secondary/helper text

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

Accessibility (WCAG 2.1 AA)

Keyboard Navigation

Every interactive element must be keyboard accessible:

tsx

// ✓ Focusable by default
<button onClick={handleClick}>Click me</button>

// ✓ Custom element with keyboard support
<div
  tabIndex={0}
  role="button"
  onKeyDown={e => { if (e.key === 'Enter' || e.key === ' ') handleClick(); }}
  onClick={handleClick}
>Click me</div>

ARIA Labels

tsx

// Label interactive elements that lack visible text
<button aria-label="Delete task" onClick={handleDelete}>
  <TrashIcon />
</button>

// Label form inputs
<label htmlFor="email">Email</label>
<input id="email" type="email" aria-describedby="email-hint" />

Focus Management

tsx

// Move focus when content changes (e.g., dialog opens)
function Dialog({ isOpen, onClose }: DialogProps) {
  useEffect(() => {
    if (isOpen) closeButtonRef.current?.focus();
  }, [isOpen]);
  // Trap focus inside dialog when open
}

Meaningful Empty and Error States

tsx

// Don't show blank screens
function TaskList({ tasks }: { tasks: Task[] }) {
  if (tasks.length === 0) {
    return (
      <div>
        <h3>No tasks yet</h3>
        <p>Get started by creating a new task.</p>
      </div>
    );
  }
  return <div>...</div>;
}

Responsive Design

Design for mobile first, then expand. Test at these breakpoints: 320px, 768px, 1024px, 1440px.

tsx

// Mobile-first responsive using Tailwind
<div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3">

Loading and Transitions

tsx

// Skeleton loading (not spinners for content areas)
function TaskListSkeleton() {
  return (
    <div>
      {Array.from({ length: 3 }).map((_, i) => (
        <div key={i} className="h-16 skeleton-pulse rounded" />
      ))}
    </div>
  );
}

// Optimistic updates for perceived speed
function useToggleTask() {
  // Update UI immediately, rollback on error
}

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.
"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, empty, error, success, and permission states handled when applicable
[ ] Follows the project's design system (spacing, colors, typography)
[ ] The rendered result passes a final UI-specific finish-gate review
[ ] No accessibility warnings in dev tools or axe-core