vercel.com↗

CSS and JavaScript in the critical path delay first paint — visitors stare at a blank screen, and Largest Contentful Paint (a Google ranking signal) suffers.

Impact — Largest Contentful Paint is a Google ranking signal. Sites in the slowest quartile of their category see 30–50% less organic search traffic than faster peers.

Large scripts block the browser’s main thread, so the page looks loaded but does not respond to taps or clicks. This is the most common cause of a slow mobile experience and directly drives up bounce rate.

Impact — Heavy JavaScript is the #1 driver of slow mobile sites — 53% of mobile users abandon pages that take longer than 3 seconds to load (Google mobile-speed research).

Accessibility issues exclude users of assistive technology and create legal exposure (ADA / European Accessibility Act). Many fixes also help SEO.

Impact — About 15% of users have a disability (WHO). Accessibility gaps both exclude these users and create ADA/EAA compliance risk in the US and EU.

Answer engines like ChatGPT, Perplexity and Claude crawl with named bots (GPTBot, ClaudeBot, Google-Extended…). With no explicit robots.txt rule you have made no decision — you neither invited them in to be cited nor kept them out. Either choice is fine; silence isn’t.

Impact — AI answer engines are a fast-growing discovery channel. Sites they can’t identify a policy for are crawled on the bot’s terms, and sites that block them forfeit citations — both are decisions worth making deliberately.

# Allow AI answer engines to read and cite your content:
User-agent: GPTBot
Allow: /

User-agent: OAI-SearchBot
Allow: /

User-agent: ChatGPT-User
Allow: /

User-agent: ClaudeBot
Allow: /

User-agent: Claude-User
Allow: /

User-agent: Google-Extended
Allow: /

User-agent: PerplexityBot
Allow: /

User-agent: Perplexity-User
Allow: /

User-agent: Applebot-Extended
Allow: /

User-agent: CCBot
Allow: /

# …or block them from training/crawling instead — pick one:
# (replace "Allow: /" with "Disallow: /" above)

Schema.org JSON-LD tells search engines and answer engines what each page is — an Organization, an Article, a Product, an FAQ. Pages with structured data earn richer search results and are easier for LLMs to summarize and cite accurately.

Impact — Structured data is a low-risk SEO and AI-visibility win: it doesn’t change your design but materially improves how engines understand and present your pages.

<script type="application/ld+json">
{
  "@context": "https://schema.org",
  "@type": "Organization",
  "name": "vercel.com",
  "url": "https://vercel.com",
  "logo": "https://vercel.com/logo.png",
  "sameAs": [
    "https://www.linkedin.com/company/your-company",
    "https://twitter.com/your-handle"
  ]
}
</script>

Oversized images waste bandwidth and slow the largest element on the page. On mobile connections this is often the single biggest load-time cost.

Impact — Images account for roughly 25% of an average mobile page (HTTP Archive). Every MB of unoptimized images adds 1–2 seconds of mobile load time.

Heavy pages cost real money for users on metered mobile data and load slowly on weak connections — a meaningful share of every site’s traffic.

Impact — Every additional megabyte of page weight typically adds 1–2 seconds of mobile load time on a slow connection (HTTP Archive).