Clerk Common Errors Skill

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: ['user@example.com'] })
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"

Resources

Next Steps

Proceed to clerk-debug-bundle for comprehensive debugging tools.

Agent Skills: Clerk Common Errors

Install this agent skill to your local

Skill Files