clerk-astro-patterns

SKILL.md

Astro Patterns

SDK: @clerk/astro v3+. Requires Astro 4.15+.

What Do You Need?

Task
Reference

Configure middleware
references/middleware.md

Protect SSR pages
references/ssr-pages.md

Use Clerk in island components
references/island-components.md

Auth in API routes
references/api-routes.md

Use Clerk with React in Astro
references/astro-react.md

Mental Model

Astro has two rendering modes per page: SSR and static prerender. Clerk works differently in each:

SSR pages — use Astro.locals.auth() which is populated by the middleware

Static pages (export const prerender = true) — Clerk middleware skips them; use client-side hooks in islands

Islands — React/Vue/Svelte components; use useAuth() and other hooks from @clerk/astro/react

Request → clerkMiddleware() → SSR page → Astro.locals.auth()
                                ↓
                         Island (.client) → useAuth() hook

Setup

astro.config.mjs

import { defineConfig } from 'astro/config'
import clerk from '@clerk/astro'

export default defineConfig({
  integrations: [clerk()],
  output: 'server',
})

src/middleware.ts

import { clerkMiddleware, createRouteMatcher } from '@clerk/astro/server'

const isProtectedRoute = createRouteMatcher(['/dashboard(.*)'])

export const onRequest = clerkMiddleware((auth, context, next) => {
  if (isProtectedRoute(context.request) && !auth().userId) {
    return auth().redirectToSignIn()
  }
  return next()
})

SSR Page Auth

---
const { userId, orgId } = Astro.locals.auth()
if (!userId) return Astro.redirect('/sign-in')
---

<h1>Dashboard</h1>

Common Pitfalls

Symptom
Cause
Fix

Astro.locals.auth is undefined
Missing middleware
Add clerkMiddleware to src/middleware.ts

Auth works in dev but not production
output: 'static' globally
Set output: 'server' or hybrid for protected pages

Static page has no auth
Prerendered pages skip middleware
Use export const prerender = false or move to island

Island not reactive to sign-in
Missing client:load directive
Add client:load to the island component

Import Map

What
Import From

clerkMiddleware, createRouteMatcher
@clerk/astro/server

useAuth, useUser, UserButton
@clerk/astro/react

Astro components (<SignIn>, etc.)
@clerk/astro/components

Env Variables

# .env
PUBLIC_CLERK_PUBLISHABLE_KEY=pk_...
CLERK_SECRET_KEY=sk_...

Astro uses PUBLIC_ prefix for client-exposed variables (not NEXT_PUBLIC_).

See Also

clerk-setup - Initial Clerk install

clerk-custom-ui - Custom flows & appearance

clerk-orgs - B2B organizations

Docs

Astro SDK