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 →
Frequently asked questions
How do I check my React app speed?
Enter your React app URL at speedexporter.com and run a Lighthouse audit. The report identifies large bundles, client-rendering LCP delays, and hydration mismatches that are common in React applications. Download the full JSON to feed to an AI agent for code-level fixes.
What causes slow LCP in React apps?
Client-side rendering (CSR) is the root cause for most React SPAs — the browser cannot render anything until the JavaScript bundle downloads, parses, and executes, typically pushing LCP beyond 4 seconds on mobile. If your app renders on the client only, no amount of image optimization will bring LCP under 2.5 seconds.
How do I pass Core Web Vitals with React?
For React SPAs, consider migrating to Next.js or Remix for server-side rendering — this is typically the single highest-impact change for LCP. If you cannot change rendering strategy, split bundles with React.lazy(), add a preload link for your LCP image, and remove unused dependencies. Export your full Lighthouse JSON and ask ChatGPT or Claude for bundle-specific recommendations.