What is Server-Side Rendering (SSR)?
A technique where web pages are generated on the server for each request, sending fully formed HTML to the browser. This improves initial load time and SEO compared to client-side rendering.
In plain English
SSR is like a restaurant that serves plated meals — the food arrives ready to eat. Client-side rendering is like a meal kit — you get raw ingredients (JavaScript) and your browser has to 'cook' the page. The plated meal (SSR) is faster to consume but takes more kitchen (server) effort.
How it works
When a user requests a page, the server runs the application code, fetches necessary data, renders the complete HTML, and sends it to the browser. The browser displays the page immediately while JavaScript 'hydrates' the page to make it interactive. This contrasts with client-side rendering (CSR) where the browser receives a blank page and JavaScript builds everything from scratch.
Why it matters for AI-built apps
SSR dramatically improves two critical metrics: perceived load speed and SEO. Search engines can index SSR pages more reliably than JavaScript-heavy SPAs. For AI-built apps using Next.js, SSR is available by default — but understanding when to use SSR vs. SSG vs. CSR for each page helps you optimize both performance and server costs.
Common issues
Hydration mismatches (server and client HTML don't match), using browser-only APIs during server rendering (window, document), slow server response times due to data fetching on every request, high server costs from rendering every page request, and not caching SSR results appropriately.
Best practices
Use SSR for dynamic, personalized pages that need SEO (product pages, blog posts). Use SSG for content that doesn't change per-request. Avoid accessing browser APIs during server rendering — use useEffect or dynamic imports. Cache SSR responses where possible. Use streaming SSR (React 18+) to send content progressively. Monitor server response times.
Frequently asked questions
Do I need SSR for my app?
If SEO matters for your pages (marketing pages, blog, product listings) — yes, SSR or SSG is important. For authenticated dashboards and internal tools, client-side rendering is fine since search engines don't need to index them. Next.js lets you mix approaches per page, so you don't have to choose one for the whole app.
Why does my Next.js page show a hydration error?
Hydration errors occur when the HTML rendered on the server doesn't match what the client renders. Common causes: using Date.now() or Math.random() during render, accessing window/localStorage during initial render, and browser extensions modifying the DOM. Fix by moving browser-specific code to useEffect hooks or using the 'use client' directive appropriately.
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