The first load of a Next.js app is a document — HTML down the wire, parsed, hydrated. But once the app is interactive, open your Network tab and you'll notice it never asks for a document again. Instead you see a trickle of odd little requests: some are GETs that return something that isn't HTML, and some are POSTs to the page you're already on, streaming a response back. Those POSTs are the part that looks weird, and they're the reason this post exists.
You type a domain, hit Enter, and a second later you're clicking around a working app. That second is deceptively busy. Between the keystroke and the first working button there's a DNS lookup, a couple of cryptographic handshakes, a streamed HTML document, a fan of parallel downloads, a serialized React tree, and a reconciliation pass that stitches JavaScript onto server-rendered markup without throwing any of it away.
Debugging a React single-page application (SPA) and debugging a Next.js App Router app are different sports, and the whole difference comes down to one thing: where your code runs. This is a recipe-oriented reference for the questions that keep coming up — where your logs went, how to see backend calls, how to observe React Server Components (RSC), and which logging options and tools are worth reaching for.
Routing in React has evolved from simple client-side navigation into a larger architectural concern. Today, routes can define not only which component appears for a URL, but also how data is loaded, how mutations happen, how errors are handled, and how layouts are nested.
You write next build, run vercel deploy, and a URL comes back. But between that command and the response your users get, there's a whole distributed system — build pipelines, an edge network, serverless and edge functions, caches at multiple layers. This post opens the box and walks through what Vercel actually does with a Next.js app.
A top-down tour of Next.js: start from the mental model of the framework as a whole, then drill into the concepts that actually shape how you build with it.
A one-line-per-concept tour of Next.js — the whole mental model at a glance, from routing to rendering to deployment, with no fluff.