UI Design

Opinionated constraints for building better interfaces with agents.

When to Use

• Building UI components with Tailwind CSS
• Implementing animations or transitions
• Adding interactive elements with keyboard/focus behavior
• Reviewing frontend code for accessibility
• Designing layouts with proper z-index and spacing
• Working with loading states, error handling, or empty states

Stack

Requirement	Rule
Tailwind CSS	MUST use defaults (spacing, radius, shadows) before custom values
Animation library	MUST use motion/react (formerly framer-motion) for JS animation
CSS animation	SHOULD use tw-animate-css for entrance and micro-animations
Class logic	MUST use cn utility (clsx + tailwind-merge)

Components

Requirement	Rule
Interactive primitives	MUST use accessible primitives (Base UI, React Aria, Radix) for keyboard/focus behavior
Existing components	MUST use project's existing primitives first
Consistency	NEVER mix primitive systems within the same interaction surface
New primitives	SHOULD prefer Base UI if compatible with stack
Icon buttons	MUST add aria-label to icon-only buttons
Custom behavior	NEVER rebuild keyboard or focus behavior by hand unless explicitly requested

Interaction

Requirement	Rule
Destructive actions	MUST use AlertDialog for destructive or irreversible actions
Loading states	SHOULD use structural skeletons
Viewport height	NEVER use h-screen, use h-dvh
Fixed elements	MUST respect safe-area-inset
Error display	MUST show errors next to where the action happens
Input behavior	NEVER block paste in input or textarea elements

Animation

Requirement	Rule
Default	NEVER add animation unless explicitly requested
Compositor props	MUST animate only transform, opacity
Layout props	NEVER animate width, height, top, left, margin, padding
Paint props	SHOULD avoid background, color except for small, local UI (text, icons)
Entrance easing	SHOULD use ease-out on entrance
Feedback timing	NEVER exceed 200ms for interaction feedback
Looping	MUST pause looping animations when off-screen
Accessibility	MUST respect prefers-reduced-motion
Custom easing	NEVER introduce custom easing curves unless explicitly requested
Large surfaces	SHOULD avoid animating large images or full-screen surfaces

Typography

Requirement	Rule
Headings	MUST use text-balance
Body text	MUST use text-pretty for paragraphs
Data	MUST use tabular-nums
Dense UI	SHOULD use truncate or line-clamp
Letter spacing	NEVER modify letter-spacing (tracking-) unless explicitly requested

Layout

Requirement	Rule
Z-index	MUST use a fixed scale (no arbitrary z-x)
Square elements	SHOULD use size-x instead of w-x + h-x

Performance

Requirement	Rule
Blur effects	NEVER animate large blur() or backdrop-filter surfaces
Will-change	NEVER apply will-change outside an active animation
useEffect	NEVER use for anything expressible as render logic

Design

Requirement	Rule
Gradients	NEVER use unless explicitly requested
Purple/multicolor gradients	NEVER use
Glow effects	NEVER use as primary affordances
Shadows	SHOULD use Tailwind CSS default scale unless explicitly requested
Empty states	MUST give one clear next action
Accent colors	SHOULD limit to one per view
Color tokens	SHOULD use existing theme or Tailwind CSS tokens before introducing new ones

Quick Reference

Allowed Animation Properties

transform, opacity

Forbidden Animation Properties

width, height, top, left, margin, padding, blur(), backdrop-filter

Required Accessibility Patterns

// Icon button - always add aria-label
<button aria-label="Close dialog">
  <XIcon />
</button>

// Respect reduced motion
@media (prefers-reduced-motion: reduce) {
  * { animation: none !important; }
}

Class Utility Pattern

import { clsx } from 'clsx';
import { twMerge } from 'tailwind-merge';

export function cn(...inputs: ClassValue[]) {
  return twMerge(clsx(inputs));
}