How to fix slow page on Headless / Custom (I build in code)

Steps for Headless / Custom (I build in code)

1. Run Lighthouse CI in your deployment pipeline to catch performance regressions automatically on every deploy.
2. Use Next.js Image component (<Image>) or equivalent framework primitives to get automatic WebP conversion, responsive srcset, and lazy loading out of the box.
3. Code-split aggressively: use dynamic imports for heavy components not needed on initial load, and tree-shake unused library code.
4. Serve all static assets through a CDN (Cloudflare, Fastly, AWS CloudFront) and set long-lived cache headers (Cache-Control: max-age=31536000, immutable) on versioned assets.
5. Enable Brotli compression at the edge/server layer and use HTTP/2 or HTTP/3.
6. Profile real-user performance with Chrome DevTools Performance tab and address the largest LCP element first, then Total Blocking Time (TBT), then Cumulative Layout Shift (CLS).

What is slow page?

Page load time is how long it takes for a visitor's browser to fully display your store page. When a page takes longer than about 3 seconds, visitors tend to leave before they even see your products — a behaviour called "bouncing." Google also directly measures loading speed as part of its Core Web Vitals scoring system, which feeds into how high your pages rank in search results. A load time of nearly 10 seconds (like the example above) is extremely slow and will hurt both rankings and sales.

Google uses Core Web Vitals — which include Largest Contentful Paint (LCP), a direct measure of loading speed — as a confirmed ranking signal. Pages that load slowly rank lower in search results, meaning fewer shoppers find you organically. Research consistently shows that every additional second of load time reduces conversion rates by roughly 4–7 %, so a 10-second page can cost you a significant share of potential sales. Slow pages also create a poor first impression, increase bounce rates, and can disqualify your pages from Google's "Page Experience" enhancements in search results. On mobile — where Google primarily indexes your site — performance issues are amplified further.

See the complete Slow page guide for every platform and the full background.