Check Your Next.js App Speed
Run a Lighthouse audit on your Next.js application and export the full JSON report. Feed it to Cursor, Claude, or ChatGPT to get exact code changes targeting your specific performance issues.
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Loading...Common performance issues on Next.js sites
These are the issues most frequently found in Next.js Lighthouse audits. Your report will tell you exactly which ones apply to your site.
Large JavaScript bundles
Client-side JavaScript is the most common performance issue in Next.js apps. The report's "Reduce unused JavaScript" audit identifies specific bundles and their sizes.
Missing image optimization
Using `<img>` instead of Next.js's `<Image>` component misses automatic WebP conversion, responsive sizing, and lazy loading — all of which impact LCP.
Cumulative Layout Shift from dynamic content
Server components that load async data without skeleton screens, or client components that hydrate differently from server HTML, frequently cause CLS issues.
Render-blocking third-party scripts
Scripts loaded without `next/script` and the `strategy` prop (afterInteractive or lazyOnload) block page rendering and increase TBT.
Pro tip: Next.js has excellent built-in tools for most performance issues: use `<Image>` for images, `next/script` for third-party scripts, and Server Components to reduce client-side JavaScript. The Lighthouse report will tell you exactly where your app is deviating from these patterns.
Want a detailed tutorial? Read our step-by-step performance fix guide →
Frequently asked questions
How do I check my Next.js app speed?
Enter your Next.js app URL at speedexporter.com and run a Lighthouse audit on mobile. The report identifies bundle size issues, missing image optimizations, and hydration-related layout shift — all common in Next.js apps. The JSON includes framework-specific StackPack hints.
What causes slow Core Web Vitals in Next.js?
The most common causes are: using a plain img tag instead of next/image (missing WebP and LCP optimization), loading third-party scripts without next/script strategy (causes render-blocking), large client-side JavaScript bundles from non-tree-shaken imports, and CLS from dynamic components that change size after hydration.
How do I fix performance issues in Next.js?
Replace all img tags with next/image for automatic WebP, responsive sizing, and LCP prioritization. Replace script tags with next/script and set strategy to afterInteractive or lazyOnload. Run next build --profile to find large bundles and split them with dynamic imports. Export your Lighthouse JSON and ask Cursor or Claude for specific component-level code changes.