Accessibility

Accessibility answers one question:

Can someone use this with assistive tools, a different input method, or a different ability?

It is specifically about people with disabilities being able to perceive, understand, navigate, and interact with a product on equal terms — whether they use a screen reader, only a keyboard, a switch, voice control, magnification, or captions. This is the ability half of designing for everyone. The context half — language, culture, device, affordability, confidence — belongs to the sibling inclusive-design skill. They overlap but have different focuses; keep them distinct so neither gets diluted.

When to use

Use this skill when the task involves any of: WCAG conformance, ARIA, semantic markup, screen-reader support, keyboard/focus management, color contrast, text alternatives (alt text, captions, transcripts), accessible forms and error messages, target sizes, timing/timeouts, motion sensitivity, or cognitive accessibility. Also use it whenever someone asks to "make this accessible," run an a11y audit, or check whether a disabled user can complete a task.

When not to use it: if the real concern is who gets left out by context — non-English speakers, people on cheap phones or slow networks, people who can't afford data, first-time or anxious users, or global name/address formats — that is inclusion, not accessibility. Switch to the inclusive-design skill.

The mental model: POUR

WCAG organizes all of accessibility under four principles. Use them as your audit lens — every issue you find maps to one of them.

• Perceivable — users can sense the content through some channel. Don't rely on one sense alone. (Text alternatives for images, captions/transcripts for audio and video, sufficient color contrast, not using color alone to convey meaning, content that reflows and survives zoom.)
• Operable — users can drive the interface with whatever input they have. (Everything reachable and usable by keyboard, visible focus, no keyboard traps, adequate target sizes, generous or adjustable time limits, nothing that flashes in a seizure-inducing way.)
• Understandable — users can predict and comprehend behavior. (Clear labels, instructions, and error messages; consistent navigation; predictable interactions; readable language.)
• Robust — assistive tech can actually parse it. (Valid semantic structure; correct name/role/value on every control; native semantics first, ARIA only to fill gaps.)

A useful test for any element: if I could not see it, hear it, use a mouse, or read quickly — could I still complete this task? If the answer is no under any of those, you've found the principle that's failing.

Who and what you are designing for

Design for the assistive tools and input methods people actually use, not an abstract "disabled user":

• Screen readers (VoiceOver, TalkBack, NVDA, JAWS) — need correct semantics, reading order, labels, and announcements of dynamic changes.
• Keyboard-only and switch users — need a logical focus order, visible focus, and no mouse-only interactions.
• Voice control — needs visible, speakable labels that match the accessible name.
• Screen magnification and zoom — needs layouts that reflow without horizontal scrolling or clipping at 200%+.
• Captions / transcripts users — Deaf and hard-of-hearing users, and anyone in a loud or silent environment.
• People with cognitive and learning disabilities — need clear language, low memory load, and forgiving flows (see below).

Note the recurring pattern: most of these help far more people than the group they target — the same insight that drives inclusive design.

Fast audit checklist

Walk these in order; each line is a concrete thing to check or fix.

1. Keyboard — Tab through the whole flow. Is every control reachable and operable? Is focus visible? Is the order logical? Can you get trapped?
2. Screen reader — Does every control announce a meaningful name and role? Are images given text alternatives (or marked decorative)? Are dynamic updates (errors, loading, toasts) announced?
3. Contrast & color — Does text meet contrast minimums (4.5:1 body, 3:1 large)? Is any meaning carried by color alone (e.g., red = error with no icon/text)?
4. Structure — Are headings, lists, landmarks/regions, and labels semantic rather than visual-only? Does reading order match visual order?
5. Forms & errors — Is every field labeled (not placeholder-only)? Are errors identified in text, tied to their field, and explained with how to fix?
6. Targets & timing — Are tap targets large enough and spaced? Are time limits absent, generous, or adjustable? Is autosave used to prevent data loss?
7. Media & motion — Captions/transcripts for audio/video? Does the UI honor reduced-motion preferences? Nothing flashing more than ~3×/second?
8. Zoom/reflow — At 200% zoom (or large system font), does content reflow without clipping or horizontal scroll?

Beyond conformance: cognitive accessibility

WCAG alone does not cover everything people with cognitive and learning disabilities (dyslexia, ADHD, autism, dementia, aphasia, memory or attention differences) need. The W3C COGA guidance is supplemental, not required for WCAG conformance, and it is where the highest-leverage improvements for the largest hidden population usually live: clear language, consistent design, single-step instructions, not relying on memory, forgiving error recovery, and minimizing distraction.

Read references/cognitive-accessibility.md for COGA's eight objectives and their concrete design patterns when the task touches readability, complex flows, forms, logins, or "this is confusing/overwhelming."

Motion, sensory, and age-related needs

Animation and motion can cause real harm (nausea, dizziness, loss of focus) for people with vestibular disorders, and seizures for people with photosensitivity. Honor the user's prefers-reduced-motion setting — reduce or replace motion rather than removing all feedback.

Older users are a large group whose age-related changes in vision, dexterity, hearing, and memory overlap directly with disability needs — designing well here helps everyone age into your product. (Treat age as a context/identity dimension — first-time confidence, life stage — in the inclusive-design skill; treat age-related ability change here.)

Read references/motion-and-sensory.md for prefers-reduced-motion patterns (with code), photosensitivity limits, and the older-user ability overlap.

How to verify

Automated checkers (axe, Lighthouse, Accessibility Scanner, etc.) catch maybe a third of issues — necessary but never sufficient. Always add manual checks: navigate the real flow with the keyboard only, then again with a screen reader, then with the OS reduced-motion and large-text settings on. The bug a tool can't catch — a focus order that makes no sense, a label that lies — is usually the one that actually blocks someone.

References

Load these only when the task calls for the depth:

• references/cognitive-accessibility.md — W3C COGA: the 8 objectives and their design patterns (beyond WCAG).
• references/motion-and-sensory.md — reduced motion (with CSS example), photosensitivity, older-user ability overlap.

Primary sources:

• Accessibility, Usability, and Inclusion — W3C WAI
• Making Content Usable for People with Cognitive and Learning Disabilities (COGA) — W3C
• Older Users and Web Accessibility — W3C WAI
• prefers-reduced-motion — MDN