Web Interface Guidelines

Review UI code according to Vercel Web Interface Guidelines.

When to Use

Use proactively when:

• UI code review requested
• Accessibility (a11y) check requested
• Design audit requested
• UX review requested
• Best practices check requested

Triggers: review UI, check accessibility, audit design, review UX, check best practices, UI review, accessibility check, design review, UX review, web guidelines, a11y check

Do NOT use for: backend code, API design, database

Usage

/web-design-guidelines src/components/Button.tsx
/web-design-guidelines "src/**/*.tsx"
/web-design-guidelines                          # prompt for file

Review Rules

Accessibility

• Icon-only buttons require aria-label
• Form controls require <label> or aria-label
• Interactive elements require keyboard handlers (onKeyDown/onKeyUp)
• Use <button> for actions, <a>/<Link> for navigation (no <div onClick>)
• Images require alt (use alt="" for decorative)
• Decorative icons require aria-hidden="true"
• Async updates (toasts, validation) require aria-live="polite"
• Prefer semantic HTML over ARIA (<button>, <a>, <label>, <table>)
• Maintain heading hierarchy <h1>–<h6>; include skip link to main content
• Anchor headings require scroll-margin-top

Focus States

• Interactive elements require visible focus: focus-visible:ring-* or equivalent
• Using outline-none / outline: none requires alternative focus indicator
• Use :focus-visible over :focus (prevents focus ring on click)
• Use :focus-within on compound controls for group focus

Forms

• Inputs require autocomplete and meaningful name
• Use correct type (email, tel, url, number) and inputmode
• Never block paste (onPaste + preventDefault)
• Labels must be clickable (htmlFor or wrap control)
• Disable spellcheck for email, code, username (spellCheck={false})
• Checkbox/Radio: label + control = single hit target (no dead zone)
• Submit button active until request starts; show spinner during request
• Errors shown inline next to field; focus first error on submit
• Placeholders end with … and show example pattern
• Use autocomplete="off" on non-auth fields (prevent password manager trigger)
• Warn on navigation with unsaved changes (beforeunload or router guard)

Animation

• Respect prefers-reduced-motion (provide reduced version or disable)
• Animate only transform/opacity (compositor-friendly)
• Forbid transition: all—list properties explicitly
• Set correct transform-origin
• SVG: transforms on <g> wrapper, transform-box: fill-box; transform-origin: center
• Animations must be interruptible—respond to user input during animation

Typography

• Use … instead of ...
• Use curly quotes " " instead of straight "
• Non-breaking spaces: 10 MB, ⌘ K, brand names
• Loading states end with …: "Loading…", "Saving…"
• Numeric columns/comparisons: font-variant-numeric: tabular-nums
• Headings: text-wrap: balance or text-pretty (prevent widows)

Content Handling

• Text containers handle long content: truncate, line-clamp-*, or break-words
• Flex children need min-w-0 (allow text truncation)
• Handle empty states—no broken UI for empty strings/arrays
• User-generated content: expect short, average, very long inputs

Images

• <img> requires explicit width and height (prevent CLS)
• Below-fold images: loading="lazy"
• Above-fold critical images: priority or fetchpriority="high"

Performance

• Large lists (>50 items): virtualize (virtua, content-visibility: auto)
• Never read layout in render (getBoundingClientRect, offsetHeight, etc.)
• Batch DOM reads/writes; avoid interleaving
• Prefer uncontrolled inputs; controlled inputs must be cheap per keystroke
• Add <link rel="preconnect"> for CDN/asset domains
• Critical fonts: <link rel="preload" as="font"> with font-display: swap

Navigation & State

• URL reflects state—filters, tabs, pagination, expanded panels in query params
• Links use <a>/<Link> (support Cmd/Ctrl+click, middle-click)
• Deep-link all state UI (consider nuqs etc. to sync URL when using useState)
• Destructive actions require confirmation modal or undo window—no instant execution

Touch & Interaction

• touch-action: manipulation (prevent double-tap zoom delay)
• Set -webkit-tap-highlight-color intentionally
• Modals/drawers/sheets: overscroll-behavior: contain
• During drag: disable text selection, inert on dragged element
• Use autoFocus carefully—desktop only, single primary input; avoid on mobile

Safe Areas & Layout

• Full-bleed layouts require env(safe-area-inset-*) for notch
• Prevent unwanted scrollbars: overflow-x-hidden on container, fix content overflow
• Prefer flex/grid over JS measurement

Dark Mode & Theming

• Dark theme requires color-scheme: dark on <html> (fixes scrollbar, inputs)
• <meta name="theme-color"> matches page background
• Native <select>: explicit background-color and color (Windows dark mode)

Locale & i18n

• Dates/times: use Intl.DateTimeFormat instead of hardcoded format
• Numbers/currency: use Intl.NumberFormat instead of hardcoded format
• Language detection: Accept-Language / navigator.languages instead of IP

Hydration Safety

• Input with value requires onChange (or use defaultValue for uncontrolled)
• Date/time rendering: prevent hydration mismatch (server vs client)
• Use suppressHydrationWarning only where truly needed

Hover & Interactive States

• Buttons/links require hover: state (visual feedback)
• Interactive states increase contrast: hover/active/focus more visible than rest

Content & Copy

• Active voice: "Install the CLI" not "The CLI will be installed"
• Title Case for headings/buttons (Chicago style)
• Numerals for counts: "8 deployments" not "eight"
• Specific button labels: "Save API Key" not "Continue"
• Error messages include fix/next step, not just problem
• Use second person; avoid first person
• Use & over "and" when space-constrained

Anti-patterns - Must Flag

• user-scalable=no or maximum-scale=1 (disables zoom)
• onPaste with preventDefault
• transition: all
• outline-none without focus-visible alternative
• Inline onClick navigation without <a>
• <div> or <span> with click handler (must use <button>)
• Images without dimensions
• Large array .map() without virtualization
• Form inputs without labels
• Icon buttons without aria-label
• Hardcoded date/number format (must use Intl.*)
• autoFocus without clear justification

AI Slop Detection - Hard Reject

AI-generated UI that looks generic must be flagged and reworked. These patterns indicate low-effort AI output:

Visual Anti-patterns (flag any occurrence)

• Purple-to-blue gradient as primary accent with no brand justification
• 3-column icon grid layout (icon + heading + paragraph x3)
• Icons inside colored circles as section markers
• "Hero image + 3 feature cards" cookie-cutter layout
• Generic stock photo placeholders or AI-generated hero images
• Overly uniform border-radius on everything (all-8px syndrome)
• Gradient CTA buttons floating in white space
• Cookie-cutter testimonial carousel (avatar + quote + name)
• Decorative blobs/mesh gradients as background filler
• "Dashboard" UI with identical stat cards in a row

Hard Rejection Criteria (immediate rework required)

• Layout is indistinguishable from a SaaS landing page template
• Color palette matches default Tailwind purple/indigo/violet without customization
• Every section follows identical padding/spacing rhythm with no visual hierarchy
• Illustrations or icons are all from the same generic set without style adaptation
• Typography uses only one weight with no clear heading/body distinction
• No brand-specific design tokens — all values are framework defaults
• Page could belong to any product — zero domain-specific visual identity

Output Format

Group by file. Use file:line format (VS Code clickable). Concise findings.

## src/Button.tsx

src/Button.tsx:42 - icon button missing aria-label
src/Button.tsx:18 - input lacks label
src/Button.tsx:55 - animation missing prefers-reduced-motion
src/Button.tsx:67 - transition: all → list properties

## src/Modal.tsx

src/Modal.tsx:12 - missing overscroll-behavior: contain
src/Modal.tsx:34 - "..." → "…"

## src/Card.tsx

✓ pass

State issue + location. Skip explanation if fix is obvious. No preamble.

Related Skills

• /react-best-practices - React/Next.js performance optimization
• /frontend-design - Frontend UI generation