Next.js App Router in Depth

Model routes with layouts

Compose nested layouts, templates, and route groups so shared UI never re-renders needlessly.

Draw the server/client line

Decide what runs on the server and what ships to the browser, and pass data across the boundary safely.

Control caching

Understand what is cached, for how long, and how to revalidate it on demand instead of guessing.

Mutate with server actions

Handle forms, validation, and optimistic updates without hand-writing an API layer.