Next.js 15 — The Complete Guide
React Server Components
React Server Components (RSC) fundamentally change the React architecture in Next.js. They execute exclusively on the server, meaning they ship zero JavaScript to the browser.
Because they never run on the client, you can securely access your database or backend microservices directly from the component body without creating a separate API route.
By default, all components in the Next.js App Router are Server Components. You only opt-in to Client Components (which do ship JS and can use state/effects) by adding the "use client" directive at the top of the file.