Accessibility (a11y)

Comprehensive accessibility guidelines based on WCAG 2.1 and Lighthouse accessibility audits. Goal: make content usable by everyone, including people with disabilities.

WCAG Principles: POUR

Principle	Description
Perceivable	Content can be perceived through different senses
Operable	Interface can be operated by all users
Understandable	Content and interface are understandable
Robust	Content works with assistive technologies

Conformance levels

Level	Requirement	Target
A	Minimum accessibility	Must pass
AA	Standard compliance	Should pass (legal requirement in many jurisdictions)
AAA	Enhanced accessibility	Nice to have

Perceivable

Text alternatives (1.1)

Images require alt text:

html

<!-- ❌ Missing alt -->
<img src="chart.png">

<!-- ✅ Descriptive alt -->
<img src="chart.png" alt="Bar chart showing 40% increase in Q3 sales">

<!-- ✅ Decorative image (empty alt) -->
<img src="decorative-border.png" alt="" role="presentation">

<!-- ✅ Complex image with longer description -->
<figure>
  <img src="infographic.png" alt="2024 market trends infographic" 
       aria-describedby="infographic-desc">
  <figcaption id="infographic-desc">
    <!-- Detailed description -->
  </figcaption>
</figure>

Icon buttons need accessible names:

html

<!-- ❌ No accessible name -->
<button><svg><!-- menu icon --></svg></button>

<!-- ✅ Using aria-label -->
<button aria-label="Open menu">
  <svg aria-hidden="true"><!-- menu icon --></svg>
</button>

<!-- ✅ Using visually hidden text -->
<button>
  <svg aria-hidden="true"><!-- menu icon --></svg>
  <span class="visually-hidden">Open menu</span>
</button>

Visually hidden class:

css

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

Color contrast (1.4.3, 1.4.6)

Text Size	AA minimum	AAA enhanced
Normal text (< 18px / < 14px bold)	4.5:1	7:1
Large text (≥ 18px / ≥ 14px bold)	3:1	4.5:1
UI components & graphics	3:1	3:1

css

/* ❌ Low contrast (2.5:1) */
.low-contrast {
  color: #999;
  background: #fff;
}

/* ✅ Sufficient contrast (7:1) */
.high-contrast {
  color: #333;
  background: #fff;
}

/* ✅ Focus states need contrast too */
:focus-visible {
  outline: 2px solid #005fcc;
  outline-offset: 2px;
}

Don't rely on color alone:

html

<!-- ❌ Only color indicates error -->
<input class="error-border">
<style>.error-border { border-color: red; }</style>

<!-- ✅ Color + icon + text -->
<div class="field-error">
  <input aria-invalid="true" aria-describedby="email-error">
  <span id="email-error" class="error-message">
    <svg aria-hidden="true"><!-- error icon --></svg>
    Please enter a valid email address
  </span>
</div>

Media alternatives (1.2)

html

<!-- Video with captions -->
<video controls>
  <source src="video.mp4" type="video/mp4">
  <track kind="captions" src="captions.vtt" srclang="en" label="English" default>
  <track kind="descriptions" src="descriptions.vtt" srclang="en" label="Descriptions">
</video>

<!-- Audio with transcript -->
<audio controls>
  <source src="podcast.mp3" type="audio/mp3">
</audio>
<details>
  <summary>Transcript</summary>
  <p>Full transcript text...</p>
</details>

Operable

Keyboard accessible (2.1)

All functionality must be keyboard accessible:

javascript

// ❌ Only handles click
element.addEventListener('click', handleAction);

// ✅ Handles both click and keyboard
element.addEventListener('click', handleAction);
element.addEventListener('keydown', (e) => {
  if (e.key === 'Enter' || e.key === ' ') {
    e.preventDefault();
    handleAction();
  }
});

No keyboard traps:

javascript

// Modal focus management
function openModal(modal) {
  const focusableElements = modal.querySelectorAll(
    'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])'
  );
  const firstElement = focusableElements[0];
  const lastElement = focusableElements[focusableElements.length - 1];
  
  // Trap focus within modal
  modal.addEventListener('keydown', (e) => {
    if (e.key === 'Tab') {
      if (e.shiftKey && document.activeElement === firstElement) {
        e.preventDefault();
        lastElement.focus();
      } else if (!e.shiftKey && document.activeElement === lastElement) {
        e.preventDefault();
        firstElement.focus();
      }
    }
    if (e.key === 'Escape') {
      closeModal();
    }
  });
  
  firstElement.focus();
}

Focus visible (2.4.7)

css

/* ❌ Never remove focus outlines */
*:focus { outline: none; }

/* ✅ Use :focus-visible for keyboard-only focus */
:focus {
  outline: none;
}

:focus-visible {
  outline: 2px solid #005fcc;
  outline-offset: 2px;
}

/* ✅ Or custom focus styles */
button:focus-visible {
  box-shadow: 0 0 0 3px rgba(0, 95, 204, 0.5);
}

Skip links (2.4.1)

html

<body>
  <a href="#main-content" class="skip-link">Skip to main content</a>
  <header><!-- navigation --></header>
  <main id="main-content" tabindex="-1">
    <!-- main content -->
  </main>
</body>

css

.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  background: #000;
  color: #fff;
  padding: 8px 16px;
  z-index: 100;
}

.skip-link:focus {
  top: 0;
}

Timing (2.2)

javascript

// Allow users to extend time limits
function showSessionWarning() {
  const modal = createModal({
    title: 'Session Expiring',
    content: 'Your session will expire in 2 minutes.',
    actions: [
      { label: 'Extend session', action: extendSession },
      { label: 'Log out', action: logout }
    ],
    timeout: 120000 // 2 minutes to respond
  });
}

Motion (2.3)

css

/* Respect reduced motion preference */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

Understandable

Page language (3.1.1)

html

<!-- ❌ No language specified -->
<html>

<!-- ✅ Language specified -->
<html lang="en">

<!-- ✅ Language changes within page -->
<p>The French word for hello is <span lang="fr">bonjour</span>.</p>

Consistent navigation (3.2.3)

html

<!-- Navigation should be consistent across pages -->
<nav aria-label="Main">
  <ul>
    <li><a href="/" aria-current="page">Home</a></li>
    <li><a href="/products">Products</a></li>
    <li><a href="/about">About</a></li>
  </ul>
</nav>

Form labels (3.3.2)

html

<!-- ❌ No label association -->
<input type="email" placeholder="Email">

<!-- ✅ Explicit label -->
<label for="email">Email address</label>
<input type="email" id="email" name="email" 
       autocomplete="email" required>

<!-- ✅ Implicit label -->
<label>
  Email address
  <input type="email" name="email" autocomplete="email" required>
</label>

<!-- ✅ With instructions -->
<label for="password">Password</label>
<input type="password" id="password" 
       aria-describedby="password-requirements">
<p id="password-requirements">
  Must be at least 8 characters with one number.
</p>

Error handling (3.3.1, 3.3.3)

html

<!-- Announce errors to screen readers -->
<form novalidate>
  <div class="field" aria-live="polite">
    <label for="email">Email</label>
    <input type="email" id="email" 
           aria-invalid="true"
           aria-describedby="email-error">
    <p id="email-error" class="error" role="alert">
      Please enter a valid email address (e.g., name@example.com)
    </p>
  </div>
</form>

javascript

// Focus first error on submit
form.addEventListener('submit', (e) => {
  const firstError = form.querySelector('[aria-invalid="true"]');
  if (firstError) {
    e.preventDefault();
    firstError.focus();
    
    // Announce error summary
    const errorSummary = document.getElementById('error-summary');
    errorSummary.textContent = `${errors.length} errors found. Please fix them and try again.`;
    errorSummary.focus();
  }
});

Robust

Valid HTML (4.1.1)

html

<!-- ❌ Duplicate IDs -->
<div id="content">...</div>
<div id="content">...</div>

<!-- ❌ Invalid nesting -->
<a href="/"><button>Click</button></a>

<!-- ✅ Unique IDs -->
<div id="main-content">...</div>
<div id="sidebar-content">...</div>

<!-- ✅ Proper nesting -->
<a href="/" class="button-link">Click</a>

ARIA usage (4.1.2)

Prefer native elements:

html

<!-- ❌ ARIA role on div -->
<div role="button" tabindex="0">Click me</div>

<!-- ✅ Native button -->
<button>Click me</button>

<!-- ❌ ARIA checkbox -->
<div role="checkbox" aria-checked="false">Option</div>

<!-- ✅ Native checkbox -->
<label><input type="checkbox"> Option</label>

When ARIA is needed:

html

<!-- Custom tabs component -->
<div role="tablist" aria-label="Product information">
  <button role="tab" id="tab-1" aria-selected="true" 
          aria-controls="panel-1">Description</button>
  <button role="tab" id="tab-2" aria-selected="false" 
          aria-controls="panel-2" tabindex="-1">Reviews</button>
</div>
<div role="tabpanel" id="panel-1" aria-labelledby="tab-1">
  <!-- Panel content -->
</div>
<div role="tabpanel" id="panel-2" aria-labelledby="tab-2" hidden>
  <!-- Panel content -->
</div>

Live regions (4.1.3)

html

<!-- Status updates -->
<div aria-live="polite" aria-atomic="true" class="status">
  <!-- Content updates announced to screen readers -->
</div>

<!-- Urgent alerts -->
<div role="alert" aria-live="assertive">
  <!-- Interrupts current announcement -->
</div>

javascript

// Announce dynamic content changes
function showNotification(message, type = 'polite') {
  const container = document.getElementById(`${type}-announcer`);
  container.textContent = ''; // Clear first
  requestAnimationFrame(() => {
    container.textContent = message;
  });
}

Testing checklist

Automated testing

bash

# Lighthouse accessibility audit
npx lighthouse https://example.com --only-categories=accessibility

# axe-core
npm install @axe-core/cli -g
axe https://example.com

Manual testing

Keyboard navigation: Tab through entire page, use Enter/Space to activate
Screen reader: Test with VoiceOver (Mac), NVDA (Windows), or TalkBack (Android)
Zoom: Content usable at 200% zoom
High contrast: Test with Windows High Contrast Mode
Reduced motion: Test with
```
prefers-reduced-motion: reduce
```
Focus order: Logical and follows visual order

Screen reader commands

Action	VoiceOver (Mac)	NVDA (Windows)
Start/Stop	⌘ + F5	Ctrl + Alt + N
Next item	VO + →	↓
Previous item	VO + ←	↑
Activate	VO + Space	Enter
Headings list	VO + U, then arrows	H / Shift + H
Links list	VO + U	K / Shift + K

Common issues by impact

Critical (fix immediately)

Missing form labels
Missing image alt text
Insufficient color contrast
Keyboard traps
No focus indicators

Serious (fix before launch)

Missing page language
Missing heading structure
Non-descriptive link text
Auto-playing media
Missing skip links

Moderate (fix soon)

Missing ARIA labels on icons
Inconsistent navigation
Missing error identification
Timing without controls
Missing landmark regions

accessibility

NPX Install

SKILL.md Content

Accessibility (a11y)

WCAG Principles: POUR

Conformance levels

Perceivable

Text alternatives (1.1)

Color contrast (1.4.3, 1.4.6)

Media alternatives (1.2)

Operable

Keyboard accessible (2.1)

Focus visible (2.4.7)

Skip links (2.4.1)

Timing (2.2)

Motion (2.3)

Understandable

Page language (3.1.1)

Consistent navigation (3.2.3)

Form labels (3.3.2)

Error handling (3.3.1, 3.3.3)

Robust

Valid HTML (4.1.1)

ARIA usage (4.1.2)

Live regions (4.1.3)

Testing checklist

Automated testing

Manual testing

Screen reader commands

Common issues by impact

Critical (fix immediately)

Serious (fix before launch)

Moderate (fix soon)

References