Accessibility

This skill is self-contained for day-to-day use. Deeper reference (needs the full harness checkout): patterns/accessibility/README.md (full examples including ARIA live regions and APG patterns). External canonical sources: WCAG 2.2 and the WAI-ARIA Authoring Practices.

Target: WCAG 2.2 Level AA.

The first rule: don't use ARIA if a native element exists

A native <button>, <a href>, <input>, <label>, <nav>, or <table> brings keyboard behavior, focus management, and the correct role/state for free. role="button" + tabindex + keyboard handler is a liability you now own forever.

<!-- Good: browser handles focus, Enter, Space, and role automatically -->
<button type="button" onclick="save()">Save</button>

<!-- Avoid: you must re-implement everything the native button provides -->
<div role="button" tabindex="0" onclick="save()" onkeydown="handleKey(event)">Save</div>

Perceivable

• Text alternatives. Meaningful images: alt describing purpose. Decorative images: alt="". Icon-only controls: aria-label or visually-hidden text.
• Contrast. Body text ≥ 4.5:1 against background. Large text (≥ 24px, or ≥ 18.66px bold) and UI components/graphics ≥ 3:1. Verify computed colors — don't eyeball.
• Color alone is not enough. A red border and an error text/icon — not red alone.

Operable

• Keyboard. All interactive elements must be reachable by Tab, in logical order, with no keyboard trap. tabindex="0" for natural order; tabindex="-1" for programmatic-only focus; never positive values.
• Visible focus. Never outline: none without a clearly visible replacement. Keyboard users navigate by it.
• Skip link. First focusable element on pages with repeated navigation: <a href="#main">Skip to main content</a>.
• Target size. Interactive targets ≥ 24×24 px (WCAG 2.2 §2.5.8), with adequate spacing if smaller.

Understandable

• Label every input. <label for> or aria-labelledby. Placeholder text is not a label — it disappears when the user starts typing.
• Errors in text. On validation failure: describe what's wrong and how to fix it; associate via aria-describedby; set aria-invalid="true" on the field.
• Consistent, predictable behavior. Focus doesn't jump unexpectedly; forms don't submit on focus change.

Robust

• Name, Role, Value for every custom widget. Follow the matching ARIA APG pattern exactly — its roles, states, and keyboard interactions. A half-implemented ARIA widget is worse than a native element.
• Announce dynamic changes. Content that updates without a page load (toasts, async results, validation) needs an aria-live region (polite for status updates, assertive only for urgent/time-sensitive changes) or role="alert".

<!-- Status message that updates asynchronously -->
<div aria-live="polite" aria-atomic="true" class="sr-only" id="status">
  <!-- Updated by JS: "3 items saved." -->
</div>

Testing: automated is not enough

Automated tools (axe-core, Lighthouse) catch ~30–50% of WCAG issues — contrast, missing labels/alt, invalid ARIA. The rest requires manual testing:

1. Tab through every interactive element — confirm logical order, visible focus, no traps.
2. Run a screen reader (NVDA + Firefox, VoiceOver + Safari) on each flow. Hear, don't just read, what's announced.
3. Check at 200% browser zoom — layout must not break or lose content.
4. Run axe-core in CI as a smoke test, not a complete audit.

Pitfalls to catch in review

// Missing alt — screen reader announces the file path
<img src="/hero.png" />  // WRONG
<img src="/hero.png" alt="Developer reviewing code" />  // RIGHT

// Form input with no label
<input type="email" placeholder="you@example.com" />  // WRONG
<label htmlFor="email">Email</label>
<input type="email" id="email" placeholder="you@example.com" />  // RIGHT

// Click handler on non-interactive element — keyboard users can't trigger
<div onClick={handleSave}>Save</div>  // WRONG
<button type="button" onClick={handleSave}>Save</button>  // RIGHT

// outline: none without a replacement focus style
button:focus { outline: none; }  // WRONG
button:focus-visible { outline: 2px solid #005fcc; outline-offset: 2px; }  // RIGHT