# Accessibility

> Audit and improve web accessibility following WCAG 2.1 guidelines. Use when asked to "improve accessibility", "a11y audit", "WCAG compliance", "screen reader support", "keyboard navigation", or "make accessible".

- Skill: `florianbruniaux/accessibility` (Agent Skill)
- Install (CLI): `npx skillmds@latest add florianbruniaux/accessibility`
- Raw SKILL.md: https://api.skillmd.com/api/skills/florianbruniaux/accessibility/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- License: MIT
- Author: FlorianBruniaux (https://skillmd.com/u/florianbruniaux)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/florianbruniaux/accessibility

---


# 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 |
|-----------|-------------|
| **P**erceivable | Content can be perceived through different senses |
| **O**perable | Interface can be operated by all users |
| **U**nderstandable | Content and interface are understandable |
| **R**obust | 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>
```

---

## 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;
}
```

### 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">
```

### 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>

<!-- ✅ 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>
```

---

## Robust

### Valid HTML (4.1.1)

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

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

### 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>
```

**When ARIA is needed:**
```html
<!-- Custom tabs component -->
<div role="tablist" aria-label="Map filters">
  <button role="tab" id="tab-1" aria-selected="true" 
          aria-controls="panel-1">Countries</button>
  <button role="tab" id="tab-2" aria-selected="false" 
          aria-controls="panel-2" tabindex="-1">Cities</button>
</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
const showNotification = (message, type = 'polite') => {
  const container = document.getElementById(`${type}-announcer`);
  container.textContent = ''; // Clear first
  requestAnimationFrame(() => {
    container.textContent = message;
  });
};
```

---

## StarMapper-specific notes

- **MapLibre canvas**: the map itself is not keyboard-navigable (known limitation). Add an accessible text description of what the map shows.
- **Popups**: MapLibre popups injected via `innerHTML` must sanitize content. Use `textContent` for user-provided data (location strings, usernames).
- **Progress indicators**: chunk loop progress bar must announce % loaded to screen readers via `aria-valuenow` + `aria-valuemin` + `aria-valuemax`.
- **Token modal**: focus must be trapped within the modal when open. Escape closes it.
- **Unmapped drawer**: animate with `transform`, respect `prefers-reduced-motion`.
- **Filter combobox**: follows ARIA combobox pattern — `role="combobox"`, `aria-expanded`, `aria-controls`.

---

## Testing checklist

### Automated testing
```bash
# Lighthouse accessibility audit
npx lighthouse https://starmapper.bruniaux.com --only-categories=accessibility

# axe-core
npm install @axe-core/cli -g
axe https://starmapper.bruniaux.com
```

### Manual testing

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

---

## Common issues by impact

### Critical (fix immediately)
1. Missing form labels
2. Missing image alt text
3. Insufficient color contrast
4. Keyboard traps
5. No focus indicators

### Serious (fix before launch)
1. Missing page language
2. Missing heading structure
3. Non-descriptive link text
4. Missing skip links

### Moderate (fix soon)
1. Missing ARIA labels on icons
2. Missing error identification
3. Missing landmark regions

## References

- [WCAG 2.1 Quick Reference](https://www.w3.org/WAI/WCAG21/quickref/)
- [WAI-ARIA Authoring Practices](https://www.w3.org/WAI/ARIA/apg/)
- [Deque axe Rules](https://dequeuniversity.com/rules/axe/)
- [Web Quality Audit](../web-quality-audit/SKILL.md)