Agent Skills: Common Accessibility (a11y) Standards

Common Accessibility (a11y) Standards

Priority: P1 (OPERATIONAL)

Accessibility is a legal requirement in the EU (Web Accessibility Directive), USA (ADA/Section 508), and many other jurisdictions. Non-compliance carries litigation risk. Target WCAG 2.2 Level AA as the minimum.

🏗 Semantic HTML First

• Use the correct HTML element before reaching for ARIA. <button>, <a>, <nav>, <main>, <section>, <form>, <label> convey semantics natively.

• Never use <div> or <span> for interactive elements — they have no keyboard role by default.

• Headings (h1–h6) must form a logical outline. One h1 per page.

• Use <button> not <div onClick>, <a> not <span onClick>, etc.

🎭 ARIA — Use Sparingly

ARIA supplements semantics when native HTML is insufficient (e.g., custom widgets). Rules:

1. No ARIA > Bad ARIA: If native HTML works, use it. ARIA only adds roles, not behavior.
2. Required attributes: Every role with required properties must include them (e.g., role="slider" needs aria-valuenow, aria-valuemin, aria-valuemax).
3. Live Regions: Use aria-live="polite" for status messages; aria-live="assertive" only for critical alerts.
4. Labels: Every form control must have a programmatic label (<label>, aria-label, or aria-labelledby).
5. Hidden content: Use aria-hidden="true" on decorative icons; never on focusable elements.

⌨️ Keyboard Navigation

• All interactive elements MUST be reachable and operable via keyboard.
• Tab order must follow visual reading order. Never use positive tabindex values (tabindex="1" breaks natural order).
• Provide visible focus indicators (see Focus style rule below).
• Modals/Dialogs: Trap focus inside when open. Return focus to trigger element on close.
• Escape key: Must close modals, dropdowns, and tooltips.
• Focus style: Never outline: none without a visible replacement (min 2px solid, 3:1 contrast).

🎨 Color & Contrast

• Normal text: ≥ 4.5:1 ratio. Large text (≥ 18pt or 14pt bold): ≥ 3:1. UI components: ≥ 3:1.
• Never convey information through color alone — add icon, pattern, or text label.
• Test with: axe DevTools, WAVE, Lighthouse.

📐 Touch & Pointer Targets

• Minimum interactive target size: 44×44px (WCAG 2.5.5 AAA) / 24×24px minimum (WCAG 2.2 AA).
• Provide sufficient spacing between adjacent targets to prevent mis-taps.

🖼 Images & Media

• Decorative images: alt="" (empty, not missing).
• Informative images: descriptive alt text (what the image conveys, not "image of...").
• Complex charts/graphs: provide a text summary or data table alternative.
• Video: Captions mandatory. Audio descriptions for visual-only content.

🧪 Testing Minimum

• CI gate: axe-core zero critical violations.
• Manual: keyboard-only full flow + screen reader (NVDA/VoiceOver) + 200% zoom.

Anti-Patterns

• No onClick on <div>: Use <button> or add role, tabindex, and keyboard handlers.
• No missing alt: Every <img> must have an alt attribute (empty string if decorative).
• No color-only status: Red = error must also show an icon or text.
• No outline: none without replacement focus style.
• No auto-playing media: Users with vestibular disorders may be harmed.
• No dynamic content without announcement: Use aria-live for async status updates.

References

• WCAG 2.2 Quick Reference
• ARIA Authoring Practices Guide
• axe-core Rules