Web Accessibility (WCAG 2.2 AA)
Build for everyone — accessibility is a requirement, not a feature.
Contrast Ratios (WCAG AA)
| Element | Minimum Ratio |
|---|
| Normal text (< 18pt) | 4.5:1 |
| Large text (>= 18pt or 14pt bold) | 3:1 |
| UI components and focus indicators | 3:1 |
WCAG 2.2 New AA Criteria
| Criterion | Requirement |
|---|
| Target Size Minimum (2.5.8) | Interactive targets at least 24x24 CSS pixels |
| Focus Not Obscured Minimum (2.4.11) | Focused element at least partially visible, not hidden by sticky headers or overlays |
| Focus Appearance (2.4.13) | Focus indicator has minimum area (2px perimeter) and 3:1 contrast change |
| Dragging Movements (2.5.7) | Provide single-pointer alternative for any drag interaction |
| Redundant Entry (3.3.7) | Do not require re-entering previously provided information |
| Consistent Help (3.2.6) | Help mechanisms (chat, phone, FAQ) appear in same relative order across pages |
| Accessible Authentication (3.3.8) | No cognitive function test for login (allow paste, autofill, or alternatives) |
Essential Keyboard Patterns
| Key | Action |
|---|
| Tab / Shift+Tab | Navigate between focusable elements |
| Enter / Space | Activate buttons and links |
| Arrow keys | Navigate within widgets (tabs, menus) |
| Escape | Close dialogs and menus |
| Home / End | Jump to first/last item in widget |
Element Selection
| Need | Element |
|---|
| Navigates to page | <a href="..."> |
| Submits form | <button type="submit"> |
| Opens dialog | <button aria-haspopup="dialog"> |
| Other action | <button type="button"> |
| Self-contained article | <article> |
| Navigation links | <nav> |
| Supplementary info | <aside> |
Common ARIA Attributes
| Attribute | Purpose |
|---|
aria-label | Name when no visible label exists |
aria-labelledby | Reference existing text as label |
aria-describedby | Additional description (hints, errors) |
aria-live | Announce dynamic updates (polite or assertive) |
aria-expanded | Collapsible/expandable state |
aria-hidden="true" | Hide decorative elements from screen readers |
aria-invalid | Mark form fields with errors |
aria-required="true" | Mark required fields |
aria-busy | Indicate loading state |
WCAG 2.2 AA Checklist Summary
| Principle | Key Requirements |
|---|
| Perceivable | Alt text on images, contrast >= 4.5:1, color not sole indicator, text resizable to 200%, captions on video, prefers-reduced-motion support |
| Operable | Keyboard accessible, visible focus not obscured, focus appearance meets minimum, targets >= 24px, skip links, dragging alternatives |
| Understandable | <html lang="en">, consistent navigation, consistent help placement, form labels, error identification, no redundant entry, accessible auth |
| Robust | Valid HTML, name/role/value on all UI components, aria-live for status messages (SC 4.1.1 Parsing is obsolete in WCAG 2.2) |
Anti-Patterns
| Anti-Pattern | Fix |
|---|
<div onClick> instead of <button> | Use semantic HTML elements |
outline: none without replacement | Use :focus-visible with visible outline |
| Placeholder as label | Use <label> element |
tabindex > 0 | Use DOM order or tabindex="0" / tabindex="-1" |
| Color-only state indicators | Add icon and text label |
| Skipped heading levels | Use sequential h1-h6, style with CSS |
role="button" on <button> | Remove redundant ARIA |
aria-hidden on interactive elements | Never hide interactive content |
| Fixed font sizes (px) | Use rem units |
| No focus trap in modal dialogs | Trap focus, close on Escape |
Common Mistakes
| Mistake | Correct Pattern |
|---|
Adding aria-label to elements that already have visible text | Use aria-labelledby to reference existing visible text instead |
Using aria-live="assertive" for non-urgent updates | Use aria-live="polite" for most dynamic content; reserve assertive for errors and alerts |
Setting alt="" on informative images | Provide descriptive alt text; only use empty alt on purely decorative images |
| Adding keyboard handlers to non-focusable elements | Use native interactive elements or add tabindex="0" plus role and key handlers |
| Testing only with automated tools like axe | Automated scans catch ~30% of issues; always supplement with keyboard-only and screen reader testing |
Screen Reader and Browser Pairings
| Screen Reader | Browser | Platform |
|---|
| JAWS | Chrome | Windows |
| NVDA | Chrome | Windows (free) |
| NVDA | Firefox | Windows (free) |
| VoiceOver | Safari | macOS / iOS |
| TalkBack | Chrome | Android |
| Narrator | Edge | Windows (built-in) |
Testing Quick Guide
| Method | Tool | Effort |
|---|
| Keyboard-only | Hide mouse, Tab through page | 5 min |
| Screen reader | JAWS + Chrome or NVDA + Chrome/Firefox | 10 min |
| Screen reader | VoiceOver + Safari (macOS) | 10 min |
| Automated scan | axe DevTools browser extension | 2 min |
| Lighthouse | Chrome F12 > Lighthouse > Accessibility | 2 min |
| Unit tests | jest-axe (Jest) or vitest-axe (Vitest) | Ongoing |
Delegation
When working on accessibility, delegate to:
design-system — Color tokens and contrast verificationreact-patterns — Component patterns and hookstesting — jest-axe integration and test patterns
Resources
References
- Semantic HTML and Structure — Document landmarks, heading hierarchy, element selection, skip links
- Focus Management — Focus indicators, focus not obscured, dialog focus traps, SPA route focus, focus-visible patterns
- ARIA Patterns — Accessible tabs, live regions, data tables with ARIA attributes
- Forms and Validation — Label association, error announcement, redundant entry, accessible authentication
- Color and Media — Contrast requirements, reduced motion, dragging alternatives, video captions, alt text
- Testing — Keyboard testing, screen reader pairings, axe DevTools, jest-axe and vitest-axe unit tests