Web Interface Guidelines

Review UI code for compliance with Vercel's web interface standards.

Quick Reference - Visual Stability

Issue	Rule
Images without dimensions	<img> needs explicit width and height (prevents CLS)
Font loading flash	Critical fonts: <link rel="preload" as="font"> with font-display: swap
Large lists	Virtualize lists >50 items (content-visibility: auto)
Layout reads in render	No getBoundingClientRect, offsetHeight in render path

Full Rules

Images

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

Performance

• Large lists (>50 items): virtualize (virtua, content-visibility: auto)
• No layout reads in render (getBoundingClientRect, offsetHeight, offsetWidth, scrollTop)
• Batch DOM reads/writes; avoid interleaving
• Add <link rel="preconnect"> for CDN/asset domains
• Critical fonts: <link rel="preload" as="font"> with font-display: swap

Accessibility

• Icon-only buttons need aria-label
• Form controls need <label> or aria-label
• Interactive elements need keyboard handlers (onKeyDown/onKeyUp)
• <button> for actions, <a>/<Link> for navigation (not <div onClick>)
• Images need alt (or alt="" if decorative)

Focus States

• Interactive elements need visible focus: focus-visible:ring-* or equivalent
• Never outline-none / outline: none without focus replacement
• Use :focus-visible over :focus (avoid focus ring on click)

Animation

• Honor prefers-reduced-motion (provide reduced variant or disable)
• Animate transform/opacity only (compositor-friendly)
• Never transition: all—list properties explicitly

Forms

• Inputs need autocomplete and meaningful name
• Use correct type (email, tel, url, number) and inputmode
• Never block paste (onPaste + preventDefault)
• Labels clickable (htmlFor or wrapping control)

Content Handling

• Text containers handle long content: truncate, line-clamp-*, or break-words
• Flex children need min-w-0 to allow text truncation
• Handle empty states—don't render broken UI for empty strings/arrays

Anti-patterns (flag these)

• user-scalable=no or maximum-scale=1 disabling zoom
• transition: all
• outline-none without focus-visible replacement
• Images without dimensions
• Large arrays .map() without virtualization
• Form inputs without labels
• Icon buttons without aria-label