Next.js 15 Interview Questions: 20 Essential Q&A to Ace Your Dev Interview in 2026
Introduction
Landing a developer job in 2026 requires more than just knowing how to code; it requires understanding the "why" behind the framework. After building several production-grade apps—often coding late into the night after a long day of work—I’ve realized that Next.js 15 brings specific shifts that interviewers love to test.
Whether you are preparing for a remote role or a local tech giant, these 20 questions cover everything from Server Components to Prisma integration.
Top 20 Next.js 15 & Full-Stack Interview Questions
1. What is the main difference between Next.js 14 and Next.js 15?
Next.js 15 introduces support for React 19, the @next/env package, and most importantly, Async Request APIs. Headers, cookies, and params are now asynchronous, requiring an await before access.
2. Explain Server Components vs. Client Components.
Server Components (default) render on the server, reducing the JavaScript bundle size. Client Components use the 'use client' directive and allow for interactivity (hooks like useState, useEffect).
3. What is Partial Prerendering (PPR)?
PPR allows you to combine static and dynamic content on the same page. You can have a static shell (fast loading) while dynamic parts (like a user's cart) are streamed in.
4. How does Middleware work in Next.js 15?
Middleware runs before a request is completed. It’s essential for RBAC (Role-Based Access Control), multi-tenant security, and redirects.
5. Why should we use Prisma with Next.js?
Prisma is a type-safe ORM. In Next.js, it allows you to write database queries directly inside Server Actions or Server Components without needing a separate backend API layer.
6. What are Server Actions?
They are asynchronous functions that run on the server. They allow you to handle form submissions and data mutations without manually creating API endpoints.
7. How do you optimize images in Next.js?
By using the <Image /> component. It provides automatic resizing, lazy loading, and serves images in modern formats like WebP. For zero-cost scaling, integrating ImageKit or Cloudinary is a pro tip.
8. What is the purpose of the layout.js file?
It defines a UI that is shared across multiple pages (like your header/footer). It preserves state and does not re-render when navigating between sibling routes.
9. Explain 'Hydration' in React/Next.js.
Hydration is the process where client-side JavaScript attaches event listeners to the static HTML sent by the server, making the page interactive.
10. How do you handle SEO in Next.js?
By using the Metadata API. You can export a metadata object or use generateMetadata for dynamic SEO titles and descriptions.
11. What is ISR (Incremental Static Regeneration)?
ISR allows you to update static pages after you’ve built your site, without needing to rebuild the entire site. You use the revalidate tag or time-based intervals.
12. How do you implement Multi-tenancy?
Using Middleware to detect the subdomain or path, and then filtering database queries (Prisma) based on the tenantId.
