accessibility
Web accessibility discipline: semantic HTML first, ARIA only when needed, keyboard access always. Invoke whenever task involves any interaction with accessible web content -- writing, reviewing, refactoring, or debugging HTML/CSS/JS for WCAG compliance, ARIA usage, keyboard navigation, focus management, screen reader support, or accessible component patterns.
What this skill does
# Accessibility
**Semantic HTML is the foundation. ARIA is the patch. Keyboard access is non-negotiable. If an element looks
interactive, it must be interactive for everyone.**
Target **WCAG 2.2 AA conformance** unless the project explicitly specifies otherwise. AA includes all A criteria.
## References
- **Semantic HTML** — [`semantic-html.md`](${CLAUDE_SKILL_DIR}/references/semantic-html.md): Landmarks, headings,
images, tables, lists, language markup
- **ARIA** — [`aria.md`](${CLAUDE_SKILL_DIR}/references/aria.md): Roles, states, properties, naming, live regions,
common mistakes
- **Keyboard** — [`keyboard.md`](${CLAUDE_SKILL_DIR}/references/keyboard.md): Focus order, visibility, roving tabindex,
focus traps, restoration
- **Forms** — [`forms.md`](${CLAUDE_SKILL_DIR}/references/forms.md): Labels, grouping, required fields, validation,
autocomplete
- **Component patterns** — [`component-patterns.md`](${CLAUDE_SKILL_DIR}/references/component-patterns.md): Dialog,
tabs, accordion, disclosure, menu, combobox, tooltip
- **WCAG** — [`wcag.md`](${CLAUDE_SKILL_DIR}/references/wcag.md): Full WCAG 2.2 AA criteria tables and compliance
checklist
---
## 1. Semantic HTML
Use the right element for the right job. Native elements provide built-in keyboard support, screen reader announcements,
and focus management that ARIA can only approximate.
### Landmarks
- Every page must have exactly one `<main>`.
- `<header>`/`<footer>` map to `banner`/`contentinfo` only as direct children of `<body>` -- nested inside `<article>`,
`<section>`, etc. they lose their landmark role.
- Label multiple `<nav>` elements with `aria-label` or `aria-labelledby`.
- Never duplicate implicit roles (`<main role="main">`, `<nav role="navigation">`).
- Include all perceivable content within a landmark region.
For the full landmark-to-role mapping table, see [`semantic-html.md`](${CLAUDE_SKILL_DIR}/references/semantic-html.md).
### Headings
- One `<h1>` per page identifying the primary content.
- Never skip heading levels -- `<h1>` then `<h3>` breaks the outline.
- Use headings for structure, not visual styling.
- Every `<section>` and major content area should begin with a heading.
### Interactive Elements
Use `<button>` for actions (submit, toggle, open dialog) -- activates via Enter and Space. Use `<a href>` for navigation
-- activates via Enter. Never `<a href="#" onclick="...">` for actions. Never `<button>` for navigation.
### Tables
- Use `<th>` with `scope="col"` or `scope="row"` for headers.
- Add `<caption>` to describe the table's purpose.
- Never use tables for layout.
### Lists
Use `<ul>` for unordered, `<ol>` for ordered, `<dl>`/`<dt>`/`<dd>` for term/description pairs. Screen readers announce
list type and item count.
### Images
- Every `<img>` must have an `alt` attribute -- even if empty.
- Do not start alt text with "Image of" or "Picture of".
- Keep alt text under ~125 characters.
- For decorative images, prefer CSS `background-image` over `<img alt="">`.
- Use real text, not images of text (WCAG 1.4.5).
For alt treatment by image type, see [`semantic-html.md`](${CLAUDE_SKILL_DIR}/references/semantic-html.md).
### Language and Page Metadata
- Set `<html lang="...">` on every page (WCAG 3.1.1).
- Mark inline language changes: `<span lang="fr">bonjour</span>` (WCAG 3.1.2).
- Expand abbreviations on first use with `<abbr>`.
- Provide a descriptive `<title>` on every page (WCAG 2.4.2).
- Provide a skip link as the first focusable element (WCAG 2.4.1).
---
## 2. ARIA
**No ARIA is better than bad ARIA.** ARIA modifies only the accessibility tree -- it does not change behavior, keyboard
interaction, or appearance.
### The Five Rules of ARIA
- **Use native HTML first.** If a semantic HTML element exists, use it.
- **Do not change native semantics** unless absolutely necessary. Never `<h2 role="tab">` -- use
`<div role="tab"><h2>...</h2></div>`.
- **All interactive ARIA controls must be keyboard operable.** A `role="button"` must respond to Enter and Space.
- **Never `role="presentation"` or `aria-hidden="true"` on focusable elements.**
- **All interactive elements must have an accessible name.**
### Naming and Describing
**Priority:** `aria-labelledby` > `aria-label` > `<label>` > element content
> `title`.
- Prefer visible labels over `aria-label`.
- Use `aria-labelledby` to compose names from multiple elements.
- `aria-label` and `aria-labelledby` replace native label text, not supplement.
- Never `aria-label` on elements with `role="presentation"` or `role="none"`.
- Never `aria-label` on `<div>` without a role -- ignored by most AT.
- Use `aria-describedby` or `aria-description` for supplementary info after the name is established.
### Live Regions
- Use `aria-live="polite"` for non-urgent updates.
- Use `aria-live="assertive"` sparingly -- only errors, alerts, urgent info.
- Set live regions in the DOM before content changes. Adding `aria-live` and content simultaneously may not be
announced.
- Inject alert content into an existing `role="alert"` container for reliable announcement.
Place `aria-expanded` on the trigger element, not the panel.
For widget roles, state/relationship attribute tables, and common ARIA mistakes, see
[`aria.md`](${CLAUDE_SKILL_DIR}/references/aria.md).
---
## 3. Keyboard Navigation
All interactive functionality must be operable with a keyboard alone.
### Fundamental Keys
Tab/Shift+Tab between components. Arrow keys within composite widgets. Enter activates links, buttons, menu items. Space
activates buttons, checkboxes, toggles. Escape closes overlays.
### Focus Order
- Never `tabindex` > 0. Rearrange DOM order instead.
- `tabindex="0"` makes non-interactive elements focusable (use sparingly).
- `tabindex="-1"` for programmatic focus only (dialog containers, skip targets).
- Source order = visual order = focus order. CSS reordering (`flex-direction: row-reverse`, `order`, grid) must not
break this.
### Focus Visibility
- Never `outline: none` without a custom focus style replacement.
- Use `:focus-visible` for keyboard-only focus styles.
- Focus indicator: at least 3:1 contrast against adjacent background.
- Focus indicator area: at least 2px border equivalent (WCAG 2.4.13).
- Focused element must not be entirely obscured (WCAG 2.4.11).
### Focus Management
Use roving tabindex for composite widgets (tabs, toolbars, menus): active child gets `tabindex="0"`, others get
`tabindex="-1"`. Use `aria-activedescendant` when the container must maintain focus (combobox).
### Focus Trap (Dialogs)
1. On open: focus first focusable element inside dialog.
2. Trap Tab/Shift+Tab -- wrap last-to-first and first-to-last.
3. Escape closes dialog.
4. On close: return focus to the trigger element.
5. Set `aria-modal="true"`.
### Focus Restoration
- **Deleted item** -- focus next item, or previous if last was deleted.
- **Closed overlay** -- focus the trigger that opened it.
- **Removed section** -- focus nearest logical container or heading.
- Never let focus fall to `document.body`.
### Disabled Elements
- Remove disabled standalone controls from tab sequence (`disabled` attribute or `tabindex="-1"`).
- Keep disabled items focusable inside composite widgets (menus, tabs, trees, listboxes) so screen reader users can
discover them.
- Use `aria-disabled="true"` to keep element focusable but not operable.
---
## 4. Accessible Forms
### Labels
Every `<input>`, `<select>`, `<textarea>` must have a programmatic label.
**Priority:** `<label for/id>` > wrapping `<label>` > `aria-labelledby` > `aria-label`.
- `placeholder` is not a label substitute -- disappears on input, unreliable in screen readers.
- Visible label text must be contained in the accessible name (WCAG 2.5.3).
### Grouping
- Group related controls with `<fieldset>` + `<legend>`. Required for: radio groups, checkbox groups, related input sets
(address, date parts).
- Use `role="group"` with `aria-labelledby` when `<fieldset>` isRelated in Design
contribute
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plaid
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