Debugging Next.js Like a Pro: Tools, Patterns, and Real-World Tactics

1. My Go-To Debugging Toolkit

Let’s start with the core tools I rely on every single time I debug:

Browser DevTools (obviously) :

Console logs, network tab, performance tab, all of them are gold when you’re tracking SSR/CSR bugs.

VSCode Debugger + Breakpoints

Setting up debugging with next dev lets me step through server functions like getServerSideProps() or API routes. Underrated, but crucial.

React Profiler

This helped me catch a brutal re-render loop once caused by a memoized function gone rogue.

Lighthouse & Web Vitals Panel

Essential for performance debugging, especially when CLS and LCP scores drop after updates.

next dev + --turbo

The new Turbo engine in Next.js speeds up reloads and surfaces more meaningful stack traces during errors.

2. Real Bug: Hydration Mismatch That Drove Me Nuts

So one day, I had this component rendering a count fetched from localStorage on the client. Looked fine locally, but once deployed, boom! Hydration mismatch.

Turns out:

SSR rendered undefined, then client rehydrated with 12, and Next.js freaked out.

Fix:

Wrapped it with useEffect + useState so it only loaded on client, problem solved.

const [count, setCount] = useState(0);
useEffect(() => {
  const stored = localStorage.getItem(’count’);
  if (stored) setCount(Number(stored));
}, []);

Lesson: Don’t access browser APIs during SSR.

3. Debugging API Routes and Middleware

Always check the Network tab, see if the API route returns the expected JSON

Use console.log(req.method) in API handlers to verify behavior

Use Postman or curl to test routes in isolation

For Middleware issues, log req.nextUrl.pathname to debug reroutes

4. Performance Debugging: When Things Are Slow

When your app is sluggish, here’s what I usually check:

Large JS bundles?

Run next build, look at output. Anything over 300kb? Time to code split.

Static Props too heavy?

Don’t fetch a 1000-row dataset in getStaticProps(). Use pagination or defer to client-side.

Too many re-renders?

Use React Profiler to see which components are over-rendering. Then optimize with memo or useCallback.

Final Thoughts

Debugging isn’t about fixing fast, it’s about understanding deeply.

Next.js has layers. If you learn how to inspect each one, from server to client to edge, you’ll feel less stuck and more in control.