What is Server-Side Rendering (SSR / SSG)?

Modern web frameworks like Next.js offer three rendering strategies. Client-Side Rendering (CSR) sends a minimal HTML shell to the browser and builds the page using JavaScript after it loads — flexible but slow for initial load and invisible to search crawlers until JavaScript executes. Server-Side Rendering (SSR) generates the full HTML on the server for each incoming request — the browser receives ready-to-display content immediately. Static Site Generation (SSG) generates HTML at build time and serves cached static files — the fastest approach, ideal for content that doesn't change per user.

The choice of rendering strategy has direct SEO implications. Google can render JavaScript, but SSR and SSG pages are more reliably indexed and score better on Core Web Vitals because the browser receives usable content immediately rather than waiting for JavaScript execution. For most content pages, SSG is optimal; for pages with user-specific data, SSR or a hybrid approach is needed.

Next.js makes this decision per-page rather than per-application. A marketing landing page can be SSG (fast, cacheable), a dashboard can use SSR or client-side rendering (user-specific), and a product listing can use Incremental Static Regeneration (ISR — SSG that revalidates periodically). This granularity is one of the primary reasons Next.js has become the default framework for serious web products.