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

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)

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

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

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Robust	Valid HTML, name/role/value on all UI components, `aria-live` for status messages (SC 4.1.1 Parsing is obsolete in WCAG 2.2)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-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

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

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

When working on accessibility, delegate to:

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