nextjs-app-router-fundamentals

App Router migration involves moving your route files from the pages/ directory to app/, creating layout.tsx for shared UI, and replacing page components with page.tsx files. The App Router uses file-based conventions (layout.tsx, page.tsx, route.ts) and supports dynamic routes, route groups, and server actions for modern Next.js 13+ development.

App Router is Next.js 13+'s file-based routing system that replaces Pages Router with a more flexible structure. It introduces layouts for nested UI, improved metadata handling via metadata exports, route groups for organization, and built-in server actions, eliminating the need for API routes in many cases.

Export a metadata object from layout.tsx or page.tsx files to configure SEO and accessibility. App Router metadata handles title, description, and other head tags automatically, improving search visibility and Open Graph support across your application.

Yes. App Router supports dynamic routes using [param] syntax and catch-all routes using [...slug] syntax in folder names. Route groups with (folderName) organize routes without affecting URL structure, enabling flexible routing patterns and layout nesting.

No. Next.js supports gradual migration—Pages Router and App Router can coexist in the same project. Start by creating new features in app/ while maintaining existing pages/ routes, then incrementally migrate page by page without stopping development.

App Router enforces strict TypeScript by default with no implicit any. Use layout.tsx and page.tsx with proper type annotations, export typed metadata objects, and define route handlers with explicit parameter types to maintain type safety across your application.