accessibility-patterns
Build inclusive web experiences following WCAG guidelines. Covers semantic HTML, ARIA, keyboard navigation, color contrast, and testing strategies. Triggers on accessibility, a11y, WCAG, screen readers, or inclusive design requests.
What this skill does
# Accessibility Patterns
Build for everyone from the start.
## Core Principles (POUR)
| Principle | Meaning | Example |
|-----------|---------|---------|
| **Perceivable** | Users can perceive content | Alt text, captions, contrast |
| **Operable** | Users can interact | Keyboard access, enough time |
| **Understandable** | Users can comprehend | Clear language, predictable |
| **Robust** | Works with assistive tech | Valid HTML, ARIA |
---
## WCAG Levels
| Level | Description | Target |
|-------|-------------|--------|
| A | Minimum | Must have |
| AA | Standard | Industry standard, legal requirement |
| AAA | Enhanced | Nice to have |
**Target Level AA** for most projects.
---
## Semantic HTML
### Use the Right Element
| Instead of | Use |
|------------|-----|
| `<div onclick>` | `<button>` |
| `<span class="link">` | `<a href>` |
| `<div class="header">` | `<header>` |
| `<div class="nav">` | `<nav>` |
| `<div class="main">` | `<main>` |
| `<b>` for emphasis | `<strong>` |
| `<i>` for emphasis | `<em>` |
### Document Structure
```html
<!DOCTYPE html>
<html lang="en">
<head>
<title>Descriptive Page Title</title>
</head>
<body>
<a href="#main" class="skip-link">Skip to main content</a>
<header>
<nav aria-label="Main">
<!-- navigation -->
</nav>
</header>
<main id="main">
<h1>Page Title</h1>
<!-- Only one h1 per page -->
<article>
<h2>Section</h2>
<h3>Subsection</h3>
</article>
</main>
<aside aria-label="Related content">
<!-- sidebar -->
</aside>
<footer>
<!-- footer content -->
</footer>
</body>
</html>
```
### Heading Hierarchy
```
h1 - Page title (one per page)
h2 - Major sections
h3 - Subsections
h4 - Sub-subsections
Never skip levels (h1 → h3)
```
---
## Images & Media
### Alt Text
```html
<!-- Informative image -->
<img src="chart.png" alt="Bar chart showing sales increased 40% in Q4">
<!-- Decorative image -->
<img src="decorative-border.png" alt="" role="presentation">
<!-- Complex image -->
<figure>
<img src="complex-diagram.png" alt="System architecture diagram">
<figcaption>
Detailed description of the system architecture...
</figcaption>
</figure>
<!-- Image as link -->
<a href="/products">
<img src="product.jpg" alt="View our products">
</a>
```
### Alt Text Guidelines
| Image Type | Alt Text Strategy |
|------------|-------------------|
| Informative | Describe content and function |
| Decorative | Empty alt="" |
| Functional | Describe the action |
| Complex | Brief alt + longer description |
| Text in image | Include all text |
### Video & Audio
```html
<!-- Video with captions -->
<video controls>
<source src="video.mp4" type="video/mp4">
<track kind="captions" src="captions.vtt" srclang="en" label="English">
<track kind="descriptions" src="descriptions.vtt" srclang="en" label="Audio descriptions">
</video>
<!-- Audio with transcript -->
<audio controls>
<source src="podcast.mp3" type="audio/mpeg">
</audio>
<a href="transcript.html">Read transcript</a>
```
---
## Forms
### Labels
```html
<!-- Explicit label (preferred) -->
<label for="email">Email address</label>
<input type="email" id="email" name="email">
<!-- Implicit label -->
<label>
Email address
<input type="email" name="email">
</label>
<!-- Required fields -->
<label for="name">
Name <span aria-hidden="true">*</span>
<span class="sr-only">(required)</span>
</label>
<input type="text" id="name" required aria-required="true">
```
### Error Handling
```html
<div role="alert" aria-live="polite">
<p>Please fix the following errors:</p>
<ul>
<li><a href="#email">Email is required</a></li>
</ul>
</div>
<label for="email">Email</label>
<input
type="email"
id="email"
aria-invalid="true"
aria-describedby="email-error"
>
<span id="email-error" class="error">Please enter a valid email address</span>
```
### Form Groups
```html
<fieldset>
<legend>Shipping Address</legend>
<label for="street">Street</label>
<input type="text" id="street">
<label for="city">City</label>
<input type="text" id="city">
</fieldset>
```
---
## Keyboard Navigation
### Focus Management
```css
/* Never remove focus outline without replacement */
:focus {
outline: 2px solid #005fcc;
outline-offset: 2px;
}
/* Custom focus style */
:focus-visible {
outline: 3px solid #005fcc;
outline-offset: 2px;
}
/* Hide outline for mouse users */
:focus:not(:focus-visible) {
outline: none;
}
```
### Tab Order
```html
<!-- Natural tab order follows DOM order -->
<!-- Use tabindex only when necessary -->
<button>First</button>
<button>Second</button>
<button>Third</button>
<!-- tabindex="0" - adds to tab order -->
<div tabindex="0" role="button">Custom interactive element</div>
<!-- tabindex="-1" - focusable via JS, not tab -->
<div tabindex="-1" id="modal">Modal content</div>
<!-- Never use tabindex > 0 -->
```
### Skip Links
```html
<a href="#main" class="skip-link">Skip to main content</a>
<style>
.skip-link {
position: absolute;
top: -40px;
left: 0;
padding: 8px;
background: #000;
color: #fff;
z-index: 100;
}
.skip-link:focus {
top: 0;
}
</style>
```
### Keyboard Patterns
| Component | Keys |
|-----------|------|
| Buttons | Enter, Space |
| Links | Enter |
| Menus | Arrows, Enter, Escape |
| Tabs | Arrows, Tab |
| Modals | Tab (trapped), Escape to close |
---
## ARIA
### When to Use ARIA
1. First, use semantic HTML
2. Then, add ARIA if needed
3. "No ARIA is better than bad ARIA"
### Common ARIA Patterns
```html
<!-- Live regions (for dynamic content) -->
<div aria-live="polite">Content updates will be announced</div>
<div aria-live="assertive">Urgent updates interrupt</div>
<!-- Expanded/collapsed -->
<button aria-expanded="false" aria-controls="menu">Menu</button>
<ul id="menu" hidden>...</ul>
<!-- Current page -->
<nav>
<a href="/" aria-current="page">Home</a>
<a href="/about">About</a>
</nav>
<!-- Busy state -->
<div aria-busy="true">Loading...</div>
<!-- Hidden from AT -->
<span aria-hidden="true">👍</span>
<!-- Labels -->
<button aria-label="Close">×</button>
<nav aria-label="Main navigation">...</nav>
<section aria-labelledby="section-heading">
<h2 id="section-heading">Section Title</h2>
</section>
```
### ARIA Roles
```html
<!-- Landmarks -->
<div role="banner">Header</div>
<div role="navigation">Nav</div>
<div role="main">Main</div>
<div role="complementary">Sidebar</div>
<div role="contentinfo">Footer</div>
<!-- Widgets -->
<div role="button">Custom button</div>
<div role="dialog" aria-modal="true">Modal</div>
<div role="tablist">Tabs</div>
<div role="alert">Error message</div>
```
---
## Color & Contrast
### Contrast Requirements
| Text Size | Level AA | Level AAA |
|-----------|----------|-----------|
| Normal text (<18px) | 4.5:1 | 7:1 |
| Large text (≥18px bold, ≥24px) | 3:1 | 4.5:1 |
| UI components | 3:1 | - |
### Color Independence
```html
<!-- Don't rely on color alone -->
<!-- Bad -->
<span style="color: red">Error</span>
<!-- Good -->
<span style="color: red">
⚠️ Error: <span class="error-text">Please enter a valid email</span>
</span>
```
### Testing Tools
- WebAIM Contrast Checker
- Chrome DevTools color picker
- Stark (Figma plugin)
- axe DevTools
---
## Testing
### Automated Testing
```javascript
// Using jest-axe
import { axe, toHaveNoViolations } from 'jest-axe';
expect.extend(toHaveNoViolations);
it('should have no accessibility violations', async () => {
const { container } = render(<MyComponent />);
const results = await axe(container);
expect(results).toHaveNoViolations();
});
```
### Manual Testing Checklist
- [ ] Navigate entire page with keyboard only
- [ ] Test with screen reader (VoiceOver, NVDA)
- [ ] Check color contrast
- [ ] Zoom to 200% - still usable?
- [ ] Disable CSS - still understandable?
- [ ] Check all images have alt text
- [ ] Verify form labels and errors
- [ ] Test focus visibility
- [ ]Related in Design
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