// the find
aidenybai/react-scan
Scan and fix React performance issues
React Scan is a drop-in performance debugger for React apps that visually highlights components that are re-rendering unnecessarily. Zero code changes required — add a script tag or npm package and you get a floating toolbar that flashes render outlines on screen. Aimed at React developers who suspect render thrash but don't want to squint at the Profiler tab.
The zero-instrumentation approach is the real win here — the CDN script works on any site including ones you don't own, which is how they pull off those demo videos showing GitHub and Twitter re-render storms. The component inspector panel shows you exactly what prop or state changed to trigger the render, which is the piece React DevTools makes annoyingly hard to find. The offscreen canvas worker for outline rendering is a smart call — it keeps the diagnostic overlay from distorting the perf numbers you're trying to measure. They've also covered every major bundler: Vite plugin, webpack, rspack, rollup, esbuild — not just the Next.js happy path.
The browser extension ships pre-built zip files checked into the repo under packages/extension/build/, which is a red flag for supply-chain hygiene — you're trusting that those zips match the source. The notifications and performance detection logic under packages/scan/src/core/notifications/ looks like it grew organically and there's no documentation on what thresholds trigger a 'slowdown' alert or how the interaction scoring works, so it's hard to trust the numbers. React Server Components are a partial blind spot — the tool works on client component trees but RSC render traces live on the server, so you'll miss a whole category of performance issues in modern Next.js apps. Test coverage is thin: a handful of unit tests on utilities and e2e specs for the overlay UI, but nothing testing the fiber-walking and render-detection core, which is the part most likely to break across React minor versions.