Fix: Invalid prerender Export in Astro

Astro shows “Invalid prerender export” when a page exports prerender in a form it can’t read while building: a let, a variable, a function call or an environment variable. Astro decides which routes to prerender by reading the source statically, before your code runs. Write it as a literal: export const prerender = false; or export const prerender = true;.

Key Takeaways

• Only export const prerender = true or = false is valid.
• let, computed values and import.meta.env lookups are not supported here.
• To decide prerendering per route programmatically, use an integration with the astro:route:setup hook.
• The hint in the error says it directly: “Mutable values declared at runtime are not supported.”

What triggers it

---
// Wrong: let instead of const
export let prerender = false;
---

---
// Wrong: computed at runtime
export const prerender = import.meta.env.PREVIEW !== 'true';
---

---
// Wrong: imported from elsewhere
import { isStatic } from '../config';
export const prerender = isStatic;
---

The fix

---
export const prerender = false;
---

Put it in the page or endpoint’s frontmatter (or at the top level of a .ts endpoint). Nothing else is required.

Setting prerender for many routes at once

If you wanted a computed value because many routes share a rule, use an integration hook instead. It runs at build time and can set prerender per route:

// astro.config.mjs
import { defineConfig } from 'astro/config';

const dynamicApi = {
  name: 'dynamic-api',
  hooks: {
    'astro:route:setup': ({ route }) => {
      if (route.component.startsWith('src/pages/api/')) {
        route.prerender = false;
      }
    },
  },
};

export default defineConfig({
  integrations: [dynamicApi],
});

Every file under src/pages/api/ now renders on demand without each one exporting prerender. You still need an adapter; see Cannot use server-side rendering without an adapter.

Different builds for preview and production

If the goal was “server-rendered in preview, static in production”, use two configs, or set output from an environment variable in astro.config.mjs (config is plain JavaScript and can read process.env). Page-level prerender must stay literal.

The hybrid rendering tip explains prerender and output together, and the Astro SSR guide covers when on-demand rendering is worth it. Astro’s integration API reference documents astro:route:setup.

FAQ

Can I use export const prerender = ‘false’ as a string?

No. It must be the boolean literal true or false.

Do I need prerender = true on static pages?

Not with the default output: 'static'. Add it only when output: 'server' is set and you want a page prerendered.