SSR vs SSG vs ISR in Next.js: The Ultimate Rendering Guide

Next.js is one of the most powerful React frameworks available today—and a big reason for its popularity is the flexibility it provides in rendering strategies. Whether you're building a static blog, a dynamic dashboard, or an e-commerce site, Next.js allows you to choose between SSR, SSG, and ISR depending on your app's needs.

In this article, we'll explore:

• What SSR, SSG, and ISR are

• Their differences and use cases

• Pros and cons of each approach

• How to choose the right rendering method

⚙️ What Are SSR, SSG, and ISR?

Let’s start by defining each rendering method and what it does.

🖥️ 1. Server-Side Rendering (SSR)

SSR means rendering the HTML on the server at runtime, on every request.

🔍 How it works:

• Every time a user accesses the page, the server generates fresh HTML.

• The browser receives a fully rendered page with data already injected.

🔧 Next.js Implementation:

export async function getServerSideProps(context) {
  const res = await fetch('<https://api.example.com/data>');
  const data = await res.json();

  return {
    props: { data }, // Passed to the page component
  };
}

✅ Pros:

• Data is always fresh.

• Great for personalized content (e.g., dashboards, user profiles).

• Better SEO than client-side rendering.

❌ Cons:

• Slower performance (due to server round-trip).

• More load on the server.

• Less cacheable.

🧑‍💻 Best For:

• Authenticated pages

• Real-time data

• Admin dashboards

📄 2. Static Site Generation (SSG)

SSG pre-renders pages at build time, meaning the HTML is generated once during deployment and served as static files.

🔍 How it works:

• Runs at build time.

• Content is fixed until you rebuild the site.

🔧 Next.js Implementation:

export async function getStaticProps() {
  const res = await fetch('<https://api.example.com/posts>');
  const posts = await res.json();

  return {
    props: { posts },
  };
}

✅ Pros:

• Lightning-fast page load (served from CDN).

• No server load at runtime.

• Fully cacheable.

❌ Cons:

• Data becomes stale until next build.

• Not ideal for frequently changing content.

🧑‍💻 Best For:

• Blogs

• Marketing pages

• Documentation

🔁 3. Incremental Static Regeneration (ISR)

ISR is Next.js’s hybrid approach—it lets you create or update static pages after deployment, without rebuilding the whole site.

🔍 How it works:

• Pages are generated at runtime on the first request (or based on time).

• Regenerated in the background after a defined time (revalidate).

• Combines performance of SSG with freshness of SSR.

🔧 Next.js Implementation:

export async function getStaticProps() {
  const res = await fetch('<https://api.example.com/posts>');
  const posts = await res.json();

  return {
    props: { posts },
    revalidate: 60, // Regenerate every 60 seconds
  };
}

✅ Pros:

• Balance between speed and data freshness.

• Scalable and cost-efficient.

• Can pre-build popular pages and defer others.

❌ Cons:

• More complex than pure SSR or SSG.

• Delay in updating content depending on revalidate time.

🧑‍💻 Best For:

• E-commerce product pages

• News sites

• Large sites with frequent updates

📊 Quick Comparison Table

🧠 How to Choose the Right Rendering Strategy

🟢 Use SSR When:

• Your data changes every second (real-time).

• You need to fetch user-specific or sensitive data.

• You want SEO benefits but can't cache the data.

🟢 Use SSG When:

• Content doesn’t change often (e.g., homepage, about page).

• You want blazing fast performance.

• You have a small to medium number of pages.

🟢 Use ISR When:

• You want the performance of SSG but with fresh data.

• Your site has thousands of pages (like a product catalog).

• You want to regenerate pages without redeploying.

🧩 Real-World Examples

✅ SSR in Action:

• E-commerce cart or checkout

• Dashboard showing user activity

• Live sports scores

✅ SSG in Action:

• Developer portfolios

• Company landing pages

• Documentation like docs.nextjs.org

✅ ISR in Action:

• Amazon-style product detail pages

• News article pages

• Blog posts with frequent updates

💬 Developer Experience in Next.js

With Next.js, switching between SSR, SSG, and ISR is effortless:

• All options live within the same file (getServerSideProps, getStaticProps, revalidate).

• No need to change routing or file structure.

• Built-in support with Vercel and other cloud platforms.

🔥 Bonus: Middleware and Edge Functions

Next.js 13+ also introduces Middleware and Edge Functions, allowing developers to:

• Personalize pages without SSR

• Rewrite/redirect based on cookies or headers

• Run logic closer to the user (geolocation, auth checks)

This complements all rendering strategies for blazing performance with smart logic.

🏁 Conclusion

Next.js provides unmatched flexibility by offering SSR, SSG, and ISR within a single framework. These rendering modes allow developers to make performance-driven decisions based on use cases rather than technical limitations.

Whether you need always fresh data, blazing fast static content, or a mix of both, Next.js has you covered.

📎 Final Tips

• Use SSR for real-time, personalized, or private content.

• Use SSG for performance-critical and static content.

• Use ISR when you need the best of both worlds—performance and up-to-date data.

By mastering these rendering modes, you can build modern, scalable, and SEO-friendly apps that delight users and perform well in production.

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