Incremental Static Regeneration (ISR)

Incremental static regeneration (ISR) is a rendering strategy, popularized by Next.js, in which pages are generated as static files but can be refreshed after the site is deployed. A page is served from cache, and once a set time has passed the next request triggers a background rebuild of just that page.

Why it matters

Pure static generation is fast but forces a rebuild for every content edit, which becomes slow on sites with thousands of pages. Pure server rendering is always fresh but costs compute on every request. ISR sits between them: visitors get static-speed responses while content stays reasonably current.

Example

// Next.js pages router
export async function getStaticProps() {
  const posts = await fetchPosts();
  return { props: { posts }, revalidate: 60 };
}

With revalidate: 60, the cached page is reused for 60 seconds. The first request after that still receives the old copy while a new version is built, and later visitors get the fresh one. This is the stale-while-revalidate pattern.

Common mistakes

• Expecting an edit to appear instantly; one more request may still show the stale page.
• Using it for personalized content, since the cached HTML is shared by everyone.
• Ignoring CDN caching, which can add a second delay on top of the revalidate time.

Related

• Next.js
• Static site generator
• Server-side rendering
• Cache-Control

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