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SKILL.md
Clerk Common Errors
Overview
Diagnose and resolve common Clerk authentication errors. Organized by error category with root cause analysis and fix code.
Prerequisites
Clerk SDK installed
Access to Clerk Dashboard for configuration verification
Browser developer tools for client-side debugging
Instructions
Error Category 1: Configuration Errors
Clerk: Missing publishableKey
// Cause: ClerkProvider not receiving key
// Fix: Ensure env var is set and accessible
// .env.local
NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY=pk_test_...
// Verify in code:
console.log('PK:', process.env.NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY) // Should not be undefined
ClerkProvider must wrap your application
// Cause: Clerk hook used outside provider
// Fix: Wrap root layout with ClerkProvider
// app/layout.tsx
import { ClerkProvider } from '@clerk/nextjs'
export default function RootLayout({ children }: { children: React.ReactNode }) {
return (
<ClerkProvider>
<html><body>{children}</body></html>
</ClerkProvider>
)
}
Error Category 2: Authentication Errors
form_identifier_not_found
// Cause: Email not registered in Clerk instance
// Fix: Check correct Clerk instance (dev vs prod) and user exists
// Diagnostic:
import { createClerkClient } from '@clerk/backend'
const clerk = createClerkClient({ secretKey: process.env.CLERK_SECRET_KEY! })
const users = await clerk.users.getUserList({ emailAddress: ['[email protected]'] })
console.log('User found:', users.totalCount > 0)
form_password_incorrect
// Cause: Wrong password or user set up with OAuth only
// Fix: Check auth strategy in Clerk Dashboard
// User may need password reset:
// Dashboard > Users > Select user > Authentication > Reset password
session_exists (Error during sign-in)
// Cause: User already has active session
// Fix: Sign out first or redirect
'use client'
import { useAuth } from '@clerk/nextjs'
import { redirect } from 'next/navigation'
export default function SignInPage() {
const { isSignedIn } = useAuth()
if (isSignedIn) redirect('/dashboard')
// ... render sign-in form
}
Error Category 3: Middleware Errors
Infinite redirect loop
// Cause: Sign-in page not in public routes
// Fix: Add auth pages to public route matcher
import { clerkMiddleware, createRouteMatcher } from '@clerk/nextjs/server'
const isPublicRoute = createRouteMatcher([
'/sign-in(.*)', // Must include sign-in
'/sign-up(.*)', // Must include sign-up
'/',
'/api/webhooks(.*)',
])
export default clerkMiddleware(async (auth, req) => {
if (!isPublicRoute(req)) await auth.protect()
})
auth() was called but Clerk middleware was not detected
// Cause: middleware.ts not in correct location or matcher not matching
// Fix: Ensure middleware.ts is at project root (not inside app/ or src/)
// Verify matcher includes the route:
export const config = {
matcher: [
'/((?!_next|[^?]*\\.(?:html?|css|js(?!on)|jpe?g|webp|png|gif|svg|ttf|woff2?|ico|csv|docx?|xlsx?|zip|webmanifest)).*)',
'/(api|trpc)(.*)',
],
}
Error Category 4: Server/Client Component Errors
useUser() in Server Component
// Error: Hooks can only be called inside a Client Component
// Fix: Use auth()/currentUser() server-side, useUser() client-side
// Server Component (no 'use client'):
import { currentUser } from '@clerk/nextjs/server'
export default async function Page() {
const user = await currentUser()
return <div>{user?.firstName}</div>
}
// Client Component (with 'use client'):
'use client'
import { useUser } from '@clerk/nextjs'
export function Profile() {
const { user } = useUser()
return <div>{user?.firstName}</div>
}
Hydration mismatch with auth state
// Cause: Server renders unauthenticated, client has session
// Fix: Use ClerkLoaded or check isLoaded before rendering auth-dependent UI
'use client'
import { useUser } from '@clerk/nextjs'
export function SafeAuthUI() {
const { user, isLoaded } = useUser()
if (!isLoaded) return <div>Loading...</div> // Prevent hydration mismatch
return <div>{user ? `Hello ${user.firstName}` : 'Not signed in'}</div>
}
Error Category 5: Webhook Errors
Invalid signature on webhook endpoint
// Cause: CLERK_WEBHOOK_SECRET mismatch or body parsing issue
// Fix 1: Verify secret matches Dashboard > Webhooks > Signing Secret
// Fix 2: Read raw body, don't use JSON middleware before verification
// Next.js App Router (correct):
export async function POST(req: Request) {
const body = await req.text() // Use text(), not json()
const wh = new Webhook(process.env.CLERK_WEBHOOK_SECRET!)
const evt = wh.verify(body, { /* svix headers */ })
}
// Express (correct):
app.post('/webhooks', express.raw({ type: 'application/json' }), handler)
// NOT: app.post('/webhooks', express.json(), handler) // This breaks signature
Output
Identified error category and root cause
Working fix code for each common error
Diagnostic steps for verification
Error Handling
Error
Cause
Quick Fix
Missing publishableKey
Env var not set
Add NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY to .env.local
auth() not detected
Middleware missing/misplaced
Move middleware.ts to project root
Redirect loop
Auth pages not public
Add sign-in/sign-up to isPublicRoute matcher
Hydration mismatch
Server/client state differs
Guard with isLoaded check
Webhook invalid signature
Body parsed before verify
Use req.text() not req.json() before wh.verify()
Examples
Quick Diagnostic Checklist
# 1. Check Clerk packages are installed
npm list @clerk/nextjs 2>/dev/null
# 2. Verify env vars are set
node -e "console.log('PK:', !!process.env.NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY, 'SK:', !!process.env.CLERK_SECRET_KEY)"
# 3. Test API connectivity
curl -s -o /dev/null -w "%{http_code}" -H "Authorization: Bearer $CLERK_SECRET_KEY" https://api.clerk.com/v1/users?limit=1
# 4. Check middleware exists at root
ls middleware.ts 2>/dev/null && echo "Found" || echo "Missing - create middleware.ts at project root"
