Next.js Rendering Strategies: CSR vs SSR vs SSG vs ISR (Complete Guide) 2025

Understanding how Next.js renders your pages is crucial for building fast, scalable, and SEO-friendly web applications. In this article, we’ll explore Client-Side Rendering (CSR), Server-Side Rendering (SSR), Static Site Generation (SSG), and Incremental Static Regeneration (ISR) — their differences, pros/cons, and when to use them.

🔍 Overview

Next.js offers four main rendering strategies:

• CSR (Client-Side Rendering): Rendering happens in the browser.
• SSR (Server-Side Rendering): HTML is rendered on each request.
• SSG (Static Site Generation): HTML is generated at build time.
• ISR (Incremental Static Regeneration): Pages are pre-built but can be revalidated after deployment.

Key Concepts

• Hydration: Turning static HTML into an interactive React app.
• FCP (First Contentful Paint): When first content appears.
• TTI (Time To Interactive): When page is fully usable.
• SEO: How search engines crawl and index your content.

⚡ Client-Side Rendering (CSR)

How it Works

1. Minimal HTML is served.
2. Browser downloads JavaScript.
3. JavaScript fetches data and renders UI.

✅ Pros & ❌ Cons

• ✅ Great for interactivity
• ✅ Light on the server
• ❌ Poor SEO (blank HTML initially)
• ❌ Slower first load

Example

"use client" import { useState, useEffect } from 'react'; export default function CSRExample() { const [posts, setPosts] = useState([]); useEffect(() => { fetch('https://jsonplaceholder.typicode.com/posts').then(res => res.json()).then(setPosts); }, []); return ( <div> <h1>Posts (CSR)</h1> {posts.map(p => <p key={p.id}>{p.title}</p>)} </div> ); } 

👉 Best For: Dashboards, private content, real-time apps.

🌐 Server-Side Rendering (SSR)

How it Works

1. Request comes in.
2. Server fetches data.
3. HTML is generated and sent.
4. Browser hydrates the page.

✅ Pros & ❌ Cons

• ✅ Fresh data every request
• ✅ Great SEO
• ❌ Slower response time
• ❌ Higher server load

Example

export async function callApi() { const res = await fetch('https://jsonplaceholder.typicode.com/posts'); const posts = await res.json(); return posts } export default async function SSRExample() { const posts = await callApi() return <ul>{posts.map(p => <li key={p.id}>{p.title}</li>)}</ul>; } 

👉 Best For: E-commerce, news, personalized content.

🚀 Static Site Generation (SSG)

How it Works

1. At build time, Next.js generates HTML.
2. Pages are cached on CDN.
3. Super-fast delivery.

✅ Pros & ❌ Cons

• ✅ Fastest load times
• ✅ Great SEO
• ✅ Very scalable
• ❌ Stale content until rebuild

Example

import { notFound } from "next/navigation"; async function getPost(id) { const res = await fetch( `https://jsonplaceholder.typicode.com/posts/${id}`, ); if (!res.ok) { return null; } return res.json(); } export async function generateStaticParams() { const res = await fetch("https://jsonplaceholder.typicode.com/posts"); const posts = await res.json(); return posts.map((post) => ({ id: post.id.toString(), })); } export default async function PostPage({ params }) { const post = await getPost(params.id); if (!post) { notFound(); } return ( <main> <h1>{post.title}</h1> <p>{post.body}</p> </main> ); } 

👉 Best For: Blogs, docs, marketing pages.

🔄 Incremental Static Regeneration (ISR)

How it Works

1. Pages are generated at build time (like SSG).
2. Pages are revalidated in the background.
3. Next visitors get the fresh content.

✅ Pros & ❌ Cons

• ✅ Speed of SSG + freshness of SSR
• ✅ No full rebuilds needed
• ❌ Temporary stale content

Example

export const revalidate = 60 import { notFound } from "next/navigation"; async function getPost(id) { const res = await fetch( `https://jsonplaceholder.typicode.com/posts/${id}`, ); if (!res.ok) { return null; } return res.json(); } export async function generateStaticParams() { const res = await fetch("https://jsonplaceholder.typicode.com/posts"); const posts = await res.json(); return posts.map((post) => ({ id: post.id.toString(), })); } export default async function PostPage({ params }) { const post = await getPost(params.id); if (!post) { notFound(); } return ( <main> <h1>{post.title}</h1> <p>{post.body}</p> </main> ); } 

👉 Best For: E-commerce catalogs, news sites, frequently updated blogs.

📊 Comparison Chart

💡 When to Use What

• CSR: Dashboards, authenticated apps, real-time updates.
• SSR: SEO + fresh content, e-commerce, user-specific pages.
• SSG: Marketing sites, blogs, documentation.
• ISR: Large sites, e-commerce catalogs, news portals.

🎯 Exercises for You

1. Pick a blog and implement SSG with dynamic routes.
2. Create a dashboard with CSR (fetch on client).
3. Build a news site homepage with ISR.
4. Compare performance using Lighthouse.

📌 Final Thoughts

Each rendering strategy in Next.js serves different needs:

• CSR = Flexibility
• SSR = Real-time + SEO
• SSG = Performance
• ISR = Balance between speed and freshness

By mixing them wisely, you can build fast, SEO-friendly, and scalable apps.

🔗 Additional Resources

• Next.js Data Fetching Docs
• Next.js API Routes
• Web Vitals