How to Test Performance in Vibecoded Apps

Run Lighthouse in Chrome DevTools on every major page of your app. Focus on the three Core Web Vitals: Largest Contentful Paint (LCP should be under 2.5 seconds), First Input Delay (FID should be under 100ms), and Cumulative Layout Shift (CLS should be under 0.1). AI-generated apps frequently score poorly on CLS because they load content dynamically without reserving space.

Test on a throttled connection (Slow 3G in DevTools) to simulate real-world conditions. Many vibecoded apps feel fast on your development machine's fast connection but are unusable on mobile networks. Record these metrics before and after changes so you can track performance over time and catch regressions.

Use a bundle analyzer (webpack-bundle-analyzer or source-map-explorer) to visualize what is in your JavaScript bundles. AI tools frequently import entire libraries when only a single function is needed — for example, importing all of lodash instead of just lodash/debounce. These unnecessary imports can add hundreds of kilobytes to your bundle.

Check for duplicate dependencies — different versions of the same library being bundled together. Also verify that code splitting is working correctly: pages that the user has not navigated to should not have their code loaded upfront. Many AI-generated Next.js apps accidentally import server-only code into client components, inflating the client bundle.

Use Chrome DevTools Performance and Memory tabs to check for memory leaks. Navigate between pages several times and take heap snapshots — if memory grows steadily without being released, you have a leak. AI-generated React apps commonly leak memory through useEffect cleanup functions that are missing or incorrect, or through event listeners that are never removed.

Profile rendering performance by recording a timeline while interacting with your app. Look for long tasks (over 50ms) that block the main thread and cause jank. Common culprits in vibecoded apps include re-rendering entire lists instead of individual items, running expensive calculations during render, and animating properties that trigger layout recalculation.