Framework-agnostic web rules: WCAG 2.2, semantic HTML, responsive layout, forms and performance.
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SKILL.md
Web Platform Design Guidelines
Framework-agnostic rules for accessible, performant, responsive web interfaces. Based on WCAG 2.2, MDN Web Docs, and modern web platform APIs.
1. Accessibility / WCAG [CRITICAL]
Accessibility is not optional. Most rules in this section map to WCAG 2.2 success criteria at Level A or AA. A small number of best-practice rules (noted inline) target Level AAA or go beyond WCAG.
1.1 Use Semantic HTML Elements
Use elements for their intended purpose. Semantic structure provides free accessibility, SEO, and reader-mode support.
Anti-pattern: Using <div> or <span> for interactive elements. Never write <div onclick> when <button> exists.
1.2 ARIA Labels on Interactive Elements
Every interactive element must have an accessible name. Prefer visible text; use aria-label or aria-labelledby only when visible text is insufficient (SC 4.1.2).
<!-- Icon-only button: needs aria-label -->
<button aria-label="Close dialog">
<svg aria-hidden="true">...</svg>
</button>
<!-- Linked by labelledby -->
<h2 id="section-title">Notifications</h2>
<ul aria-labelledby="section-title">...</ul>
<!-- Redundant: visible text is enough -->
<button>Save Changes</button> <!-- No aria-label needed -->
1.3 Keyboard Navigation
All interactive elements must be reachable and operable via keyboard (SC 2.1.1).
Use native interactive elements (<button>, <a href>, <input>, <select>) which are keyboard-accessible by default.
Custom widgets need tabindex="0" to enter tab order and keydown handlers for activation.
Never use tabindex values greater than 0.
Trap focus inside modals; return focus on close.
// Focus trap for modal
dialog.addEventListener('keydown', (e) => {
if (e.key === 'Tab') {
const focusable = dialog.querySelectorAll(
'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])'
);
const first = focusable[0];
const last = focusable[focusable.length - 1];
if (e.shiftKey && document.activeElement === first) {
e.preventDefault();
last.focus();
} else if (!e.shiftKey && document.activeElement === last) {
e.preventDefault();
first.focus();
}
}
});
1.4 Visible Focus Indicators
Never remove focus outlines without providing a visible replacement (SC 2.4.7, enhanced SC 2.4.11 (AA) and SC 2.4.12 (AAA) in WCAG 2.2).
Identify and describe errors in text (SC 3.3.1). Link error messages to inputs with aria-describedby or aria-errormessage.
<label for="email">Email</label>
<input id="email" type="email" aria-describedby="email-error" aria-invalid="true">
<p id="email-error" role="alert">Enter a valid email address, e.g. name@example.com</p>
1.10 ARIA Live Regions
Announce dynamic content changes to screen readers (SC 4.1.3).
<!-- Polite: announced when user is idle -->
<div aria-live="polite" aria-atomic="true">
3 results found
</div>
<!-- Assertive: interrupts current speech -->
<div role="alert">
Your session will expire in 2 minutes.
</div>
<!-- Status messages -->
<div role="status">
File uploaded successfully.
</div>
Use aria-live="polite" by default. Reserve role="alert" / aria-live="assertive" for time-sensitive warnings.
1.11 ARIA Role Quick Reference
Role
Purpose
Native Equivalent
button
Clickable action
<button>
link
Navigation
<a href>
tab / tablist / tabpanel
Tab interface
None
dialog
Modal
<dialog>
alert
Assertive live region
None
status
Polite live region
<output>
navigation
Nav landmark
<nav>
main
Main landmark
<main>
complementary
Aside landmark
<aside>
search
Search landmark
<search> (HTML5)
img
Image
<img>
list / listitem
List
<ul>/<li>
heading
Heading (with aria-level)
<h1>-<h6>
menu / menuitem
Menu widget
None
tree / treeitem
Tree view
None
grid / row / gridcell
Data grid
<table>
progressbar
Progress
<progress>
slider
Range input
<input type="range">
switch
Toggle
<input type="checkbox">
Rule: Prefer native HTML over ARIA. Use ARIA only when no native element exists for the pattern.
1.12 Label in Name (WCAG 2.5.3 Level A)
When an interactive element has visible text, its accessible name must contain that visible text as a substring (SC 2.5.3). Voice control users (Dragon NaturallySpeaking, macOS Voice Control) speak the visible label to activate controls. If aria-label replaces or contradicts the visible text, voice commands fail.
<!-- Correct: aria-label contains visible text as substring -->
<button aria-label="Delete item from cart">Delete</button>
<!-- Correct: no aria-label needed — visible text is the accessible name -->
<button>Save Changes</button>
<!-- Correct: icon button — no visible text, aria-label is fine -->
<button aria-label="Close dialog">
<svg aria-hidden="true">...</svg>
</button>
<!-- Incorrect: aria-label overrides visible text with different text -->
<button aria-label="Remove">Delete</button>
<!-- Incorrect: aria-label does not contain visible "Submit" -->
<button aria-label="Proceed to next step">Submit</button>
Rule: When visible text is present, aria-label must include that visible text (verbatim, case-insensitively). Prefer no aria-label at all when visible text is sufficient.
2. Responsive Design [CRITICAL]
2.1 Mobile-First Approach
Write base styles for the smallest viewport. Layer complexity with min-width media queries.
Minimum 44x44 CSS pixels for touch targets (WCAG SC 2.5.5 AAA; SC 2.5.8 requires only 24x24px at AA). Provide at least 24px spacing between adjacent targets.
button, a, input, select, textarea {
min-height: 44px;
min-width: 44px;
}
/* Enlarge tap area without changing visual size */
.icon-button {
position: relative;
width: 24px;
height: 24px;
}
.icon-button::after {
content: "";
position: absolute;
inset: -10px; /* expands clickable area */
}
Indicate required fields visually and programmatically. Use required attribute and visible markers.
<label for="name">
Full name <span aria-hidden="true">*</span>
<span class="sr-only">(required)</span>
</label>
<input id="name" type="text" required autocomplete="name">
If most fields are required, indicate which are optional instead.
3.7 Submit Button State
Do not disable the submit button. Instead, validate on submit and show errors.
<!-- Good: always enabled, validate on submit -->
<button type="submit">Create Account</button>
<!-- Bad: disabled button with no explanation -->
<!-- <button type="submit" disabled>Create Account</button> -->
Disabled buttons fail to communicate why the user cannot proceed. If you must disable, provide a visible explanation.
3.8 Keep Instructions Near the Field
Place format examples, constraints, and recovery text next to the relevant field via hint and error text. Never explain requirements only once in introductory copy and expect users to remember them later.
4. Typography [HIGH]
4.1 Font Stacks
Use system font stacks for performance, or web fonts with proper fallbacks.
/* System font stack */
body {
font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
}
/* Monospace stack */
code, pre, kbd {
font-family: ui-monospace, "Cascadia Code", "Source Code Pro", Menlo, Consolas, monospace;
}
/* Web font with fallbacks and size-adjust */
@font-face {
font-family: "CustomFont";
src: url("/fonts/custom.woff2") format("woff2");
font-display: swap;
font-weight: 100 900;
}
body {
font-family: "CustomFont", system-ui, sans-serif;
}
4.2 Relative Units
Use rem for font sizes and spacing. Use em for component-relative sizing.
After a user action, acknowledge the new state immediately. If work cannot finish within a brief moment, show progress, skeletons, optimistic UI, or aria-busy feedback instead of leaving the interface unchanged.
6. Animation and Motion [MEDIUM]
6.1 Respect prefers-reduced-motion
Always provide a reduced-motion alternative (SC 2.3.3, Level AAA).
/* Define animations normally */
.fade-in {
animation: fadeIn 300ms ease-out;
}
@keyframes fadeIn {
from { opacity: 0; transform: translateY(8px); }
to { opacity: 1; transform: translateY(0); }
}
/* Remove or reduce for users who prefer it */
@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;
}
}
// Check in JavaScript
const prefersReducedMotion = window.matchMedia('(prefers-reduced-motion: reduce)').matches;
6.2 Compositor-Friendly Animations
Animate only transform and opacity for smooth 60fps animation. These run on the GPU compositor thread.
/* Or use CSS filter for simple cases */
@media (prefers-color-scheme: dark) {
.decorative-img {
filter: brightness(0.9) contrast(1.1);
}
}
7.6 Respect prefers-contrast
Honor the user's contrast preference using @media (prefers-contrast: more) and @media (prefers-contrast: forced). prefers-contrast: more responds to macOS/iOS "Increase Contrast" in System Settings; prefers-contrast: forced responds to Windows High Contrast Mode — a distinct OS feature that overrides colors entirely.
/* Default theme */
:root {
--color-text: #555770;
--color-border: #d1d1e0;
--color-bg: #ffffff;
}
/* High contrast mode: stronger text and border colors */
@media (prefers-contrast: more) {
:root {
--color-text: #1a1a2e; /* Darker text for higher ratio */
--color-border: #1a1a2e; /* Stronger borders */
--color-bg: #ffffff;
}
/* Ensure interactive elements are clearly delineated */
button, input, select, textarea {
border: 2px solid currentColor;
}
}
/* Forced colors (Windows High Contrast mode) */
@media (prefers-contrast: forced) {
/* Use system color keywords to respect OS color palette */
:root {
--color-text: ButtonText;
--color-bg: ButtonFace;
--color-border: ButtonBorder;
}
}
8. Navigation and State [MEDIUM]
8.1 URL Reflects State
Every meaningful view should have a unique URL. Users should be able to bookmark, share, and reload any state.
// Update URL without full page reload
function updateFilters(filters) {
const params = new URLSearchParams(filters);
history.pushState(null, '', `?${params}`);
renderResults(filters);
}
// Restore state from URL on load
const params = new URLSearchParams(location.search);
const initialFilters = Object.fromEntries(params);
// Disable browser auto-restoration for manual control
if ('scrollRestoration' in history) {
history.scrollRestoration = 'manual';
}
// Save scroll position before navigation
function saveScrollPosition() {
sessionStorage.setItem(`scroll-${location.pathname}`, window.scrollY);
}
// Restore on back/forward
window.addEventListener('popstate', () => {
const saved = sessionStorage.getItem(`scroll-${location.pathname}`);
if (saved) {
requestAnimationFrame(() => window.scrollTo(0, parseInt(saved)));
}
});
9. Touch and Interaction [MEDIUM]
9.1 Touch-Action for Scroll Control
Use touch-action to control gesture behavior on interactive elements.
/* Allow only vertical scrolling (disable horizontal pan and pinch-zoom) */
.vertical-scroll {
touch-action: pan-y;
}
/* Carousel: horizontal scroll only */
.carousel {
touch-action: pan-x;
}
/* Canvas/map: disable all browser gestures */
.canvas {
touch-action: none;
}
9.2 Tap Highlight
Control the tap highlight on mobile WebKit browsers.
button, a {
-webkit-tap-highlight-color: transparent;
}
9.3 Hover and Focus Parity
Every hover interaction must also work with keyboard focus.
Set lang on the <html> element. Use dir="auto" for user-generated content.
<html lang="en" dir="ltr">
<!-- User-generated content: let browser detect direction -->
<p dir="auto">User-submitted text here</p>
<!-- Explicit override for known RTL content -->
<blockquote lang="ar" dir="rtl">...</blockquote>
10.2 Intl APIs for Formatting
Use the Intl API for locale-aware formatting. Never hard-code date or number formats.
// Dates
new Intl.DateTimeFormat('en-US', { dateStyle: 'long' }).format(date);
// "January 15, 2026"
// Numbers
new Intl.NumberFormat('de-DE', { style: 'currency', currency: 'EUR' }).format(1234.56);
// "1.234,56 EUR"
// Relative time
new Intl.RelativeTimeFormat('en', { numeric: 'auto' }).format(-1, 'day');
// "yesterday"
// Lists
new Intl.ListFormat('en', { style: 'long', type: 'conjunction' }).format(['a', 'b', 'c']);
// "a, b, and c"
// Plurals
const pr = new Intl.PluralRules('en');
const suffixes = { one: 'st', two: 'nd', few: 'rd', other: 'th' };
function ordinal(n) { return `${n}${suffixes[pr.select(n)]}`; }
10.3 Avoid Text in Images
Text in images cannot be translated, resized, or read by screen readers. Use HTML/CSS text with background images when a styled text overlay is needed.
10.4 CSS Logical Properties
Use logical properties instead of physical ones to support both LTR and RTL layouts.
/* Physical (breaks in RTL) */
/* margin-left: 1rem; padding-right: 2rem; border-left: 1px solid; */
/* Logical (works in LTR and RTL) */
.sidebar {
margin-inline-start: 1rem;
padding-inline-end: 2rem;
border-inline-start: 1px solid var(--color-border);
}
.stack > * + * {
margin-block-start: 1rem;
}
/* Logical shorthands */
.box {
margin-inline: auto; /* left + right */
padding-block: 2rem; /* top + bottom */
inset-inline-start: 0; /* left in LTR, right in RTL */
border-start-start-radius: 8px; /* top-left in LTR, top-right in RTL */
}
Physical
Logical
left / right
inline-start / inline-end
top / bottom
block-start / block-end
margin-left
margin-inline-start
padding-right
padding-inline-end
border-top-left-radius
border-start-start-radius
width
inline-size
height
block-size
text-align: left
text-align: start
10.5 RTL Layout Support
Test layouts in RTL mode. Flexbox and Grid handle RTL automatically with logical properties.
/* This layout works in both LTR and RTL without changes */
.layout {
display: flex;
gap: 1rem;
}
/* Icons that indicate direction need flipping */
[dir="rtl"] .arrow-icon {
transform: scaleX(-1);
}
11. Progressive Web Apps [MEDIUM]
PWAs allow web apps to be installed and run offline. When building an installable web app, the following rules ensure the experience is consistent and reliable.
11.1 Provide a Complete Web App Manifest
Include a manifest.json linked from <head> with all required fields for installability. Missing fields silently prevent install prompts.
{
"name": "My App"
// Missing start_url, display, and icons — app is not installable
}
11.2 Set theme_color and background_color
theme_color tints the browser chrome and the OS task switcher. background_color fills the splash screen before the app loads. Both must match your brand colors.
11.3 Register a Service Worker for Offline Support
A service worker is required for installability and offline capability. Cache critical assets on install; respond from cache when offline.
// In your main entry point
if ('serviceWorker' in navigator) {
navigator.serviceWorker.register('/sw.js');
}
// sw.js — cache on install, serve from cache when offline
const CACHE = 'v1';
const PRECACHE = ['/', '/index.html', '/app.js', '/app.css'];
self.addEventListener('install', e =>
e.waitUntil(caches.open(CACHE).then(c => c.addAll(PRECACHE)))
);
self.addEventListener('fetch', e =>
e.respondWith(
caches.match(e.request).then(hit => hit ?? fetch(e.request))
)
);
11.4 Meet Installability Criteria
For the browser install prompt to appear: the app must be served over HTTPS, have a registered service worker with a fetch handler, and include a manifest with name, icons, start_url, and display: standalone (or fullscreen/minimal-ui).
11.5 Use display Mode Appropriately
Value
Use When
standalone
App replaces browser UI; most common choice
fullscreen
Games or media apps needing the entire screen
minimal-ui
Retain minimal browser controls (back, reload)
browser
No installation behavior; opens in browser tab
Evaluation Checklist
Use this checklist when building or reviewing web interfaces.
Accessibility
All images have appropriate alt text
Color contrast meets 4.5:1 (text) and 3:1 (UI components)
All interactive elements are keyboard accessible
Focus indicators are visible (3:1 contrast, 2px minimum perimeter)
Skip navigation link is present
Form inputs have associated labels
Error messages are linked to their inputs
Dynamic content updates use ARIA live regions
No content flashes more than 3 times per second
Page has proper heading hierarchy (h1-h6, no skips)
Landmarks are used correctly (main, nav, header, footer)
Responsive
No horizontal scrolling at 320px width
Touch targets are at least 44x44px
Viewport meta tag is present (no user-scalable=no)
Layout works on mobile, tablet, and desktop
Text is readable without zooming on mobile
Forms
All inputs have visible labels
Autocomplete attributes are set for common fields
Correct input types trigger correct mobile keyboards
Error messages are clear and specific
Required fields are indicated
Submit button is not disabled
Performance
Below-fold images use loading="lazy"
Images have explicit width and height
Critical fonts are preloaded
Third-party origins use preconnect
Large JS bundles are code-split
Motion and Theming
prefers-reduced-motion is respected
Animations use only transform and opacity
Dark mode maintains contrast ratios
color-scheme meta tag is present
Theme uses CSS custom properties
prefers-contrast: more increases text and border contrast
prefers-contrast: forced uses system color keywords
Internationalization
lang attribute on <html>
CSS logical properties used (not physical)
Dates/numbers formatted with Intl APIs
No text embedded in images
Layout tested in RTL mode
Progressive Web App
Web App Manifest linked from <head> with name, icons, start_url, and display
theme_color and background_color match brand palette
Service worker registered with a fetch handler for offline support
