SSR vs CSR — Which Rendering Strategy Should You Use?

2025-08-24

Understanding rendering strategies helps you deliver fast, SEO-friendly, and maintainable web apps. Here’s a concise guide to SSR vs CSR.

What is CSR (Client-Side Rendering)?

The server sends a minimal HTML shell and a JavaScript bundle. The browser downloads JS, builds the UI, and fetches data. First paint can be fast, but content may be blank until hydration completes.

Pros:

• Great for rich, highly interactive apps
• Can cache static assets on CDN
• Simple hosting (static + API)

Cons:

• Slower Time to First Byte (TTFB) and First Contentful Paint (FCP)
• SEO depends on prerendering/bot support
• Heavier JS on the client

CSR example (React):

function Products() {
  const [items, setItems] = React.useState([]);
  React.useEffect(() => {
    fetch('/api/products').then(r => r.json()).then(setItems);
  }, []);
  return items.map(p => <div key={p.id}>{p.name}</div>);
}

What is SSR (Server-Side Rendering)?

HTML is rendered on the server per request (or edge) and sent to the browser. Users see content earlier; hydration attaches interactivity on the client.

Pros:

• Better FCP/LCP and perceived performance
• SEO-friendly out of the box
• Personalized content at request time

Cons:

• Higher server cost/complexity
• Longer TTFB if server/data is slow
• Still ships client JS for interactivity

SSR example (Next.js):

// pages/products.js (Next 12/13 pages router)
export async function getServerSideProps() {
  const res = await fetch('https://api.example.com/products');
  const items = await res.json();
  return { props: { items } };
}
export default function Page({ items }) {
  return items.map(p => <div key={p.id}>{p.name}</div>);
}

Performance and SEO

• CSR: use code-splitting, lazy, and route-based bundles; prefetch data and cache aggressively.
• SSR: stream HTML, cache at the edge, and avoid slow blocking calls. Hydrate only what’s interactive.

Key metrics: TTFB (server), FCP/LCP (paint), TTI (hydration/JS), CLS (layout stability).

When to choose which?

• Choose CSR when: app is SPA-like, authentication heavy, and SEO is limited or handled via prerendering.
• Choose SSR when: SEO matters, content must be visible fast, or you need per-request personalization.

Hybrids and modern options

• SSG/ISR: pre-render at build time and revalidate for scale.
• Islands/Partial Hydration (Astro): render most HTML on server, hydrate only interactive islands—great DX and performance.
• Edge SSR/Streaming: reduce latency and show content progressively.

Summary

There’s no one-size-fits-all. Use SSR for content-first and SEO; use CSR for app-first interactivity. Many stacks mix both for the best user experience.