Server-Side Rendering (SSR)

Server-side rendering (SSR) means the HTML of a page is assembled on the server and arrives in the browser already complete. The opposite is client-side rendering (CSR), where the server sends a nearly empty page and JavaScript running in the browser fills in the content. The distinction sounds technical, but it has a direct impact on speed, SEO, and the user experience.

SSR has two main advantages. First, speed to first view - the user sees content sooner because they aren't waiting for a large JavaScript bundle to download and run. Second, SEO and sharing: search engines and social networks get full HTML straight away, so they don't have to rely on JavaScript finishing. For content sites, e-shops, and landing pages where rankings and fast loading matter, that's a big win.

SSR has a cost too. The server has to build the page on every request, which is more load than serving a static file. So in practice it's often combined with caching or with other modes - static generation (SSG), where pages are pre-built at build time, and incremental regeneration (ISR), which refreshes static pages after an interval. After the HTML is delivered, hydration happens: JavaScript attaches to the finished HTML and brings the interactive parts to life.

Modern frameworks like Next.js, Nuxt, and SvelteKit let you mix these modes page by page. A static blog post is pre-generated, a user dashboard is rendered on the client, a product page is rendered on the server with caching. The choice isn't all-or-nothing - it's a decision made for each part of the site based on what makes sense.