Next.js App Router
Next.js 13+'s file-system router built on React Server Components — replaces the Pages Router for new projects.
The App Router uses `app/` directory layout with React Server Components by default. Each `page.tsx` is a Server Component unless marked `'use client'`. It introduces nested layouts, parallel routes, intercepting routes, route groups, server actions, and streaming. Metadata API (`export const metadata`) and Viewport API replace next/head. As of Next 14+ the App Router is the recommended default for new B2B SaaS apps.
Related terms
A React 19+ rendering model where components run on the server, returning a serialized tree to the client — zero JS for static parts.
Next.js / React 19 server functions that run on the server but can be called from a client component as if they were local — eliminates the API-route boilerplate for forms and mutations.
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