Astro V6 Upgrade

Astro v6 Upgrade Guide

This skill is based on the final Astro v6 upgrade guide and the Cloudflare adapter v13 migration.

Quick Start

1. Check Node version: Astro v6 requires Node 22.12.0 or higher. Check with node -v, and update .nvmrc / deployment config if needed. Ensure that you include CI workflows in this update if applicable.
2. Upgrade Astro and official integrations together:

   npx @astrojs/upgrade      # npm
   pnpm dlx @astrojs/upgrade # pnpm
   yarn dlx @astrojs/upgrade # yarn
   

3. Check for legacy content collections (see below). v5 supported legacy collections via backwards-compat even without the flag. v6 removes that entirely.
4. If deploying to Cloudflare: the @astrojs/cloudflare v13 upgrade has significant changes. Load cloudflare.md.
5. Fix any errors using this guide.

Check: Legacy Content Collections

Before upgrading, check if the project needs content-collection migration. Many v5 projects silently relied on legacy backwards-compat (no flag required) and will break on v6.

Decision tree:

1. Does src/content/config.{js,ts,mjs,mts} exist?
   • Yes → needs migration (legacy config location).
2. Are there content folders in src/content/ but no config file anywhere?
   • Yes → needs migration (implicit legacy collections).
3. Otherwise, check src/content.config.{js,ts,mjs,mts} for:
   • Any collection without a loader property → needs migration.
   • Any collection with type: set → needs migration.
4. Does the code use getEntryBySlug(), getDataEntryById(), entry.slug, or entry.render()?
   • Yes → needs migration.

If any apply, load content-collections.md.

Temporary escape hatch (if migration can't happen immediately):

export default defineConfig({
  legacy: {
    collectionsBackwardsCompat: true,
  },
});

This preserves the v4-style behavior: src/content/config.ts location, type: 'content'/'data' without loaders, entry.slug, entry.render(), path-based IDs. It is explicitly a migration helper and should be removed as soon as the project moves to the Content Layer API.

Note: The old legacy.collections: true flag is removed. Remove it if present.

Quick Fixes

These are simple renames/replacements. Apply directly.

ViewTransitions → ClientRouter

---
// Before
import { ViewTransitions } from 'astro:transitions';
// After
import { ClientRouter } from 'astro:transitions';
---

<!-- Before -->
<ViewTransitions />
<!-- After -->
<ClientRouter />

Also remove the handleForms prop if present - it is now removed entirely (form handling has been built in by default since v4).

Astro.glob() → import.meta.glob()

---
// Before
const posts = await Astro.glob('./posts/*.md');

// After - note: no longer returns a Promise
const posts = Object.values(import.meta.glob('./posts/*.md', { eager: true }));
---

Consider content collections for content, or fast-glob for runtime globbing.

Zod imports

// Before (deprecated)
import { z } from 'astro:content';
import { z } from 'astro:schema';

// After
import { z } from 'astro/zod';

astro:schema and z from astro:content are deprecated - import z from astro/zod directly. For Zod 4 API changes (string formats, error messages, transforms), see zod.md.

Deprecated APIs

// Astro.site in getStaticPaths → import.meta.env.SITE
export function getStaticPaths() {
  const site = import.meta.env.SITE;  // was Astro.site
}

// Astro.generator in getStaticPaths → just remove it

// import.meta.env.ASSETS_PREFIX → astro:config/server
import { build } from 'astro:config/server';
const prefix = build.assetsPrefix;

Removed: emitESMImage()

// Before
import { emitESMImage } from 'astro/assets/utils';
const result = await emitESMImage(imageId, false, false);

// After
import { emitImageMetadata } from 'astro/assets/utils';
const result = await emitImageMetadata(imageId);

Removed: <ClientRouter /> handleForms prop

Forms are handled automatically since v4. Remove the prop:

<!-- Before -->
<ClientRouter handleForms />
<!-- After -->
<ClientRouter />

Removed: prefetch() with option

// Before
prefetch('/about', { with: 'fetch' });
// After
prefetch('/about');

Removed: rewrite() from Actions context

// Inside an Action handler - remove any context.rewrite() calls.
// Use custom endpoints instead if you need redirect/rewrite behavior.

Removed: exposed astro:transitions internals

If imported, remove these or use plain string event names:

// Before
import {
  createAnimationScope,
  isTransitionBeforePreparationEvent,
  TRANSITION_AFTER_SWAP,
} from 'astro:transitions/client';

console.log(isTransitionBeforePreparationEvent(event));
console.log(TRANSITION_AFTER_SWAP);

// After
console.log(event.type === 'astro:before-preparation');
console.log('astro:after-swap');
// createAnimationScope has no replacement - remove it.

Removed: exposed astro:actions internals

serializeActionResult and deserializeActionResult are no longer exported from astro:actions. Use getActionContext() in middleware:

import { defineMiddleware } from 'astro:middleware';
import { getActionContext } from 'astro:actions';

export const (context, next) => {
  const { serializeActionResult, deserializeActionResult } = getActionContext(context);
  // ...
});

Also remove imports of: ACTION_ERROR_CODES, ActionInputError, appendForwardSlash, astroCalledServerError, callSafely, formDataToObject, getActionQueryString, type Actions, type ActionAccept, type AstroActionContext, type SerializedActionResult.

Removed: CommonJS config files

astro.config.cjs and astro.config.cts are no longer supported. Rename to .mjs, .js, .ts, or .mts.

Changed: getStaticPaths params must be strings

// Before - numbers were auto-stringified
return [{ params: { id: 1 } }];
// After - must be string or undefined
return [{ params: { id: "1" } }];

Changed: Session driver config

// Before
import { defineConfig } from 'astro/config';

export default defineConfig({
  session: {
    driver: 'redis',
    options: { url: process.env.REDIS_URL },
  },
});

// After
import { defineConfig, sessionDrivers } from 'astro/config';

export default defineConfig({
  session: {
    driver: sessionDrivers.redis({ url: process.env.REDIS_URL }),
  },
});

Removed: Percent-encoding in route filenames

%25 is no longer allowed in filenames. Rename any src/pages/test%25file.astro etc.

Error Quick Reference

Deep Dive Files

Load these only when needed:

Experimental Flags to Remove

These flags are now stable, default, or renamed. Remove from config:

export default defineConfig({
  experimental: {
    // Remove all of these - now stable or default:
    csp: true,                     // stable: use `security.csp`
    fonts: true,                   // stable
    liveContentCollections: true,  // stable
    preserveScriptOrder: true,     // now default - see behavior-changes.md
    staticImportMetaEnv: true,     // now default - see behavior-changes.md
    headingIdCompat: true,         // now default - see behavior-changes.md
    failOnPrerenderConflict: true, // renamed to `prerenderConflictBehavior`
  },
});

Official Adapter Upgrades

All official adapters need a major upgrade alongside Astro v6 (to accompany Vite 7 + Environment API):

• @astrojs/cloudflare → v13 (significant breaking changes - see cloudflare.md)
• @astrojs/netlify
• @astrojs/node
• @astrojs/vercel

Resources

• Astro v6 Upgrade Guide
• Astro v6 Blog Post
• Content Layer Deep Dive
• Cloudflare adapter docs