Why your Next.js site is slow (and it isn't React)

Every quarter a client forwards us a Lighthouse score and blames React. It's almost never React. In five years of App Router production sites, the three culprits are always the same.

1. Uncached CMS fetches at request time App Router server components make it trivially easy to fetch data inside a component that runs on every request. If your CMS client doesn't cache and your page has six components each fetching the same story, you're making six network round-trips on every page load.

2. Images served at wrong dimensions The Next.js Image component handles resizing, but only if you give it accurate width and height props. CMS-driven images often have dynamic dimensions. Skipping those props forces layout shift, tanking your CLS score.

3. Third-party scripts on the main thread Analytics, chat widgets, and A/B testing SDKs loaded synchronously block the main thread. Move everything to next/script with strategy=lazyOnload unless it absolutely must run before paint.