How do you decide whether a Next.js component should be a server component or a client component?

Server vs client components in Next.js

Explains Next.js server/client component boundaries, interactivity, data access, serialization, and bundle impact.

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I would keep a component as a server component when it can render from server-side data without browser-only interactivity. Server components can fetch data on the server, avoid shipping that component's JavaScript to the browser, and keep secrets or backend-only calls off the client. I would use a client component when it needs state, event handlers, effects, browser APIs, or interactive behavior.

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Next.js app model, server components, client components, interactivity, data fetching, serialization, and bundle size.

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Why this question matters
Next.js interviews often test whether candidates understand the server/client boundary instead of adding use client everywhere.
I would keep a component as a server component when it can render from server-side data without browser-only interactivity. Server components can fetch data on the server, avoid shipping that component's JavaScript to the browser, and keep secrets or backend-only calls off the client. I would use a client component when it needs state, event handlers, effects, browser APIs, or interactive behavior.
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I would place the client boundary as low as practical. A page can be mostly server-rendered while a small search box, menu, or form is client-rendered. Props passed from server to client components must be serializable, so functions and complex server-only objects do not cross that boundary. If a client component needs data changes after interaction, it can call a route handler, server action, or API depending on the app architecture.

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Details

Adding use client to an entire page by default.
Passing non-serializable props from server to client components.
Trying to use browser APIs in server components.
Fetching user-specific server data with unsafe caching.

How do you decide whether a Next.js component should be a server component or a client component?

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