Check Your React App Speed
Run a Lighthouse audit on your React application and get the full JSON report. Use it with ChatGPT, Claude, or Cursor to identify and fix client-side rendering bottlenecks, bundle size issues, and Core Web Vitals problems.
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Loading...Common performance issues on React sites
These are the issues most frequently found in React Lighthouse audits. Your report will tell you exactly which ones apply to your site.
Excessive JavaScript bundle size
React apps are often over-bundled. The "Reduce unused JavaScript" audit in the report identifies specific modules you can code-split, lazy-load, or eliminate.
Large Contentful Paint from client-side rendering
React apps that render on the client (CSR) have a fundamentally high LCP because the browser must download, parse, and execute JavaScript before rendering visible content.
Hydration mismatches causing layout shift
When server-rendered HTML doesn't match client-rendered output, browsers repaint — causing CLS. The report identifies elements causing layout shift.
Missing resource hints
React apps rarely include `<link rel="preload">` for critical resources, meaning the browser discovers fonts, images, and API data later than it should.
Pro tip: If your React app has poor LCP (over 4 seconds), the root cause is often client-side rendering itself — not any individual optimization. Consider migrating to Next.js or Remix for server-side rendering. The Lighthouse report's stackPacks field includes React-specific hints for every failing audit.
Want a detailed tutorial? Read our step-by-step performance fix guide →