SSR vs CSR Detector Guide
Learn how to quickly identify whether a website uses SSR (Server-Side Rendering), CSR (Client-Side Rendering), or SSG (Static Site Generation), and understand why rendering mode matters for SEO, Core Web Vitals, and crawler indexing.
1) Three Rendering Modes: SSR / CSR / SSG
- SSR (Server-Side Rendering): Generates complete HTML on the server for each request. Best for dynamic content and personalization. Examples: Next.js getServerSideProps, Nuxt server routes.
- CSR (Client-Side Rendering): Server returns minimal HTML shell + JavaScript bundle. Content is rendered by browser after JS execution. Examples: Create React App, Vue CLI (without SSR).
- SSG (Static Site Generation): Pre-generates all HTML at build time. Serves static files directly. Best for content that rarely changes. Examples: Next.js getStaticProps, Astro, Gatsby.
html
<!-- SSR/SSG output: complete HTML -->
<body>
<div id="root">
<h1>Developer SEO Hub</h1>
<p>Free SEO tools for developers.</p>
</div>
<script src="/app.js"></script>
</body>
<!-- CSR output: minimal HTML shell -->
<body>
<div id="root"></div>
<script src="/app.js"></script>
<!-- Content appears only after JS execution -->
</body>2) Why Rendering Mode Affects SEO
While Google can execute JavaScript, CSR sites face several potential issues:
- Delayed Indexing: Googlebot must wait for JS execution before seeing content, potentially delaying indexing by hours or days.
- Worse LCP / FID: CSR typically has slower First Contentful Paint and Largest Contentful Paint, hurting Core Web Vitals scores.
- JS Error Risk: If JS bundle fails to load or throws errors, crawlers may only see a blank page.
- Social Sharing Previews: Facebook/Twitter crawlers don't execute JS, so CSR sites may fail to show OG images/titles.
javascript
// CSR: Crawlers see empty initial HTML
// View Source shows only:
<div id="root"></div>
// SSR/SSG: Crawlers see full content immediately
<div id="root">
<h1>Complete Title</h1>
<p>Complete Content</p>
</div>3) How to Detect Rendering Mode and Framework
- Open the SSR vs CSR Detector and enter the URL to analyze.
- The tool checks HTML source, JS bundles, HTTP headers, and framework signatures (e.g., __NEXT_DATA__, nuxt, hydration markers).
- Results show:
- Rendering mode (SSR / CSR / SSG / Hybrid)
- Detected framework (Next.js / Nuxt / Astro / React / Vue, etc.)
- Hydration status (presence of hydration errors)
- Recommendations (e.g., "Consider SSR or prerendering")
- If CSR and SEO matters, consider:
- Upgrade to SSR framework (e.g., Next.js App Router, Nuxt 3)
- Use prerendering services (e.g., prerender.io, Cloudflare prerendering)
- Dynamic Rendering (serve prerendered HTML to crawlers, CSR to users)
4) Hydration and Common Issues
SSR/SSG frameworks typically perform hydration (attaching client-side framework to server-rendered HTML). Common hydration failure causes:
- Server/client HTML mismatch: Server generates
<div>A</div>, but client JS expects<div>B</div>. - useEffect / componentDidMount DOM changes: Modifying DOM structure during hydration process.
- Third-party script interference: Ad or analytics scripts inserting DOM nodes before hydration completes.
javascript
// ❌ Wrong: server/client inconsistency
function MyComponent() {
const [mounted, setMounted] = useState(false);
useEffect(() => setMounted(true), []);
return <div>{mounted ? 'Client' : 'Server'}</div>;
// server HTML: <div>Server</div>
// client wants: <div>Client</div> → Hydration mismatch!
}
// ✅ Correct: use suppressHydrationWarning or ensure consistency
function MyComponent() {
return <div suppressHydrationWarning>{new Date().toISOString()}</div>;
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FAQ
SSR vs CSR detection and best practices.