Choosing between Astro static or SSR rendering is a per-page decision, not a per-site one. Prerender (static) any page whose content is the same for every visitor and can wait for a rebuild. Render on demand only pages that read cookies or headers, or that must show data fresher than your last build. If just one component on a page is personal, keep the page static and make that component a server island. Most Astro sites end up 95% static.
Key Takeaways
- Default to static: it’s the fastest, cheapest and least fragile option.
- Use on-demand rendering for per-visitor content and data that changes faster than you can rebuild.
- Use a server island when only one part of a page is dynamic.
- Client-side fetching suits small public data on static pages.
The decision in five questions
Ask these for each page, in order. Stop at the first “yes”.
- Does the page show different content to different visitors? (logged-in state, cart, personal data)
- Only one component does → server island.
- Most of the page does → on-demand.
- Must the data be fresher than your rebuild time? (stock, prices, live scores)
- Small, public data → static + client-side fetch.
- Core content of the page → on-demand with short CDN caching.
- Does the page handle a form submission with a full-page response? → on-demand (or a static page calling an action from a script).
- Is the URL space unknown at build time? (search results, arbitrary IDs) → on-demand.
- None of the above? → static.
The options side by side
| Mode | How | Needs adapter | Cached at CDN | Best for |
|---|---|---|---|---|
| Static | Default | No | Yes, fully | Marketing pages, blogs, docs, product pages |
| Static + client fetch | <script> or island calling an API |
No | Page yes, data per API | Small live bits: stock count, latest release |
| Static + server island | server:defer on one component |
Yes | Page yes, island optionally | Avatar, cart count, personalised block |
| On-demand | export const prerender = false |
Yes | With Cache-Control |
Account pages, dashboards, search, auth |
| Mostly on-demand | output: 'server' + prerender = true on static pages |
Yes | Per page | App-like sites with a few static pages |
Examples
| Page | Mode | Why |
|---|---|---|
| Home page | Static | Same for everyone |
| Blog post | Static | Rebuild on publish is fast enough |
| Product page with live stock | Static + server island or client fetch | Only the stock line changes |
| Pricing page with a currency switcher | Static | Switch in the browser |
| Account settings | On-demand | Per-user data behind a login |
| Search results | On-demand | Unknown queries |
| Contact form with thank-you page | Static + action from script, or on-demand | Depends on JS preference |
| Docs | Static | Content changes with deploys |
What each choice costs
Static pages are files on a CDN. First byte is fast everywhere, there’s nothing to crash, and hosting is often free. The cost is staleness: content updates need a rebuild, which a CMS webhook can trigger.
On-demand pages run code per request. You get fresh data and access to cookies, but you pay in hosting (functions or a server), cold starts on some platforms, slower first bytes than a CDN file, and more ways to fail. Caching headers recover much of the speed for public pages.
Server islands split the difference: a static, cacheable page with one component fetched per request after load.
Setting it up
// astro.config.mjs: keep the default static output, add an adapter
import node from '@astrojs/node';
export default defineConfig({ adapter: node({ mode: 'standalone' }) });---
// src/pages/account.astro
export const prerender = false;
---The full mechanics are in mixing static and on-demand pages and the Astro SSR guide. Hosting differences are in the Astro deploy guide.
Komal themes are fully static Astro 7 sites, so every page starts on the fastest option. Add an adapter only when a page needs it. Browse Astro themes.
FAQ
Is SSR better for SEO than static in Astro?
No. Both send complete HTML to crawlers. Static pages are usually faster, which helps.
Can I switch a page between static and SSR later?
Yes. Add or remove export const prerender = false. Dynamic routes need getStaticPaths() when static.
The official explanation of each mode is in the on-demand rendering docs.