UI/UX Best Practices Frontend Design

Comprehensive UI/UX and frontend design best practices guide. Contains 42 rules across 8 categories, prioritized by impact to guide accessible, performant, and user-friendly interface development.

When to Apply

Reference these guidelines when:

• Structuring HTML for accessibility and semantics
• Writing CSS for responsive layouts and visual hierarchy
• Optimizing images and fonts for Core Web Vitals
• Designing forms with proper validation and error handling
• Adding animations and interactive elements

Rule Categories by Priority

access-

cwv-

layout-

resp-

typo-

color-

form-

anim-

Quick Reference

1. Accessibility & WCAG Compliance (CRITICAL)

• access-semantic-html

  - Use semantic HTML elements for screen readers

• access-keyboard-navigation

  - Ensure full keyboard navigation

• access-focus-indicators

  - Provide visible focus indicators

• access-alt-text

  - Provide meaningful alt text for images

• access-aria-labels

  - Use ARIA labels for icon-only controls

• access-target-size

  - Ensure minimum touch target size (24×24px)

• access-heading-hierarchy

  - Maintain logical heading hierarchy

2. Core Web Vitals Optimization (CRITICAL)

• cwv-optimize-lcp

  - Optimize Largest Contentful Paint under 2.5s

• cwv-minimize-cls

  - Minimize Cumulative Layout Shift under 0.1

• cwv-improve-inp

  - Improve Interaction to Next Paint under 200ms

• cwv-responsive-images

  - Serve responsive images with srcset

• cwv-lazy-load-offscreen

  - Lazy load offscreen images and iframes

• cwv-critical-css

  - Inline critical CSS and defer the rest

3. Visual Hierarchy & Layout (HIGH)

• layout-visual-hierarchy

  - Establish clear visual hierarchy

• layout-whitespace

  - Use whitespace to improve readability

• layout-f-pattern

  - Design for F-pattern reading behavior

• layout-grid-system

  - Use a consistent grid system

• layout-single-cta

  - Limit to one primary CTA per screen

• layout-proximity-grouping

  - Group related elements with proximity

4. Responsive & Mobile-First Design (HIGH)

• resp-mobile-first

  - Design mobile-first with min-width queries

• resp-fluid-typography

  - Use fluid typography with clamp()

• resp-container-queries

  - Use container queries for components

• resp-touch-targets

  - Size touch targets for mobile (44×44px)

• resp-viewport-meta

  - Configure viewport meta tag correctly

5. Typography & Font Loading (MEDIUM-HIGH)

• typo-font-display

  - Use font-display to control loading behavior

• typo-preload-fonts

  - Preload critical web fonts

• typo-readable-line-length

  - Constrain line length (45-75ch)

• typo-line-height

  - Set appropriate line height (1.5-1.7)

• typo-system-font-stack

  - Use system font stack for UI elements

6. Color & Contrast (MEDIUM)

• color-contrast-ratio

  - Meet WCAG contrast ratio requirements (4.5:1)

• color-not-only-indicator

  - Never use color alone to convey information

• color-dark-mode

  - Support dark mode with prefers-color-scheme

• color-semantic-palette

  - Use semantic color names in design tokens

7. Forms & Validation UX (MEDIUM)

• form-inline-validation

  - Use inline validation after field blur

• form-error-messages

  - Write actionable error messages

• form-labels-above

  - Place labels above input fields

• form-input-types

  - Use correct HTML input types for mobile

• form-autocomplete

  - Enable browser autocomplete with correct attributes

8. Animation & Performance (LOW-MEDIUM)

• anim-gpu-properties

  - Animate only GPU-accelerated properties

• anim-will-change

  - Use will-change sparingly for animation hints

• anim-reduced-motion

  - Respect user motion preferences

• anim-duration-easing

  - Use appropriate animation duration and easing

How to Use

Read individual reference files for detailed explanations and code examples:

• Section definitions - Category structure and impact levels
• Rule template - Template for adding new rules
• Example: access-semantic-html

Full Compiled Document

For the complete guide with all rules expanded: AGENTS.md