Next.js 16 App Router Deep Dive

Who this is for

You've shipped a Pages Router app and you've tried the App Router at least once. You found use client confusing the first time, got it the second time, and are now ready to learn what's actually happening under the hood.

What makes Next.js 16 different

Three things you don't get from a "App Router Intro" blog post:

• Cache Components — 'use cache', cacheTag, cacheLife, updateTag. The full mental model, including when you should reach for them and when you absolutely shouldn't.
• Middleware as a function — Routing Middleware became a Fluid Compute function you can reason about. We'll trace a request through it.
• Streaming isn't automatic — it looks automatic, it isn't, and debugging a page that "just stopped streaming" is miserable if you don't know the model.

What we're building

One real app: a bookmark manager with public sharing, full-text search, and per-user caching. Small enough to hold in your head, realistic enough to expose every rough edge.