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mediumSystem Design

How does Next.js decide between static and dynamic rendering at build time?

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01

Understand the problem

Automatic detection based on APIs and data usage.

nextjsrenderingstaticdynamic
02

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Nudge consolestandby

Stuck? Beam a request up — the console returns a conceptual nudge that guides your logic without spoiling the implementation.

03

Study the solution

At build, Next.js analyzes each route: if it uses no dynamic functions and only cached data, it's prerendered statically; if it uses cookies/headers/searchParams or uncached fetches, it's marked dynamic. Segment config can force either mode.

Solution ready — 2 min read

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04

Read the code

Reading the build output
$ next build
Route (app)                     Size
○ /                             (Static)   prerendered as static HTML
● /blog/[slug]                  (SSG)      prerendered via generateStaticParams
ƒ /dashboard                    (Dynamic)  server-rendered on demand
# ○ Static  ● SSG  ƒ Dynamic — check this to catch accidental dynamic routes
05

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Dossier 19 of 95 decoded in the Next.js track. One more won't hurt.

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