Rendering

Rendering is how a browser (or server) takes source code—HTML, CSS, JavaScript—and turns it into the pixels you see. In server-side rendering (SSR), the server builds the complete HTML before sending it to the browser, so the page is immediately visible. In client-side rendering (CSR), the browser receives mostly empty HTML and JavaScript, then runs that code locally to generate the page content.

For SEO, rendering method matters significantly. Search engines need to see the final rendered HTML to index page content accurately. SSR typically delivers fully-formed HTML that crawlers can read on first request, while CSR requires crawlers to execute JavaScript—something not all search engines do reliably. A page that looks perfect in your browser might be invisible to search engines if rendering happens entirely on the client side and the crawler doesn't wait for or execute the JavaScript.

In practice, SEO teams often audit rendering strategy as part of technical audits, use tools like Google's Mobile-Friendly Test or Lighthouse to see what a crawler actually receives, and may recommend SSR, hydration, or pre-rendering for JavaScript-heavy sites to ensure content is discoverable.