clerk-nextjs-skills

Name: clerk-nextjs-skills
Rating: 5 (9 reviews)
Author: gocallum

by @gocallum in Development

# Install this skill:

npx skills add gocallum/nextjs16-agent-skills --skill "clerk-nextjs-skills"

Install specific skill from multi-skill repository

# Description

Clerk authentication for Next.js 16 (App Router only) with proxy.ts setup, migration from middleware.ts, environment configuration, and MCP server integration.

# SKILL.md

name: clerk-nextjs-skills
description: Clerk authentication for Next.js 16 (App Router only) with proxy.ts setup, migration from middleware.ts, environment configuration, and MCP server integration.

Quick Start

1. Install Dependencies (Using pnpm)

pnpm add @clerk/nextjs
# For MCP server integration, also install:
pnpm add @vercel/mcp-adapter @clerk/mcp-tools

2. Create proxy.ts (Next.js 16)

The proxy.ts file replaces middleware.ts from Next.js 15. Create it at the root or in /src:

// proxy.ts (or src/proxy.ts)
import { clerkMiddleware } from '@clerk/nextjs/server'

export default clerkMiddleware()

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)(.*)',
  ],
}

3. Set Environment Variables

Create .env.local in your project root:

NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY=your_publishable_key_here
CLERK_SECRET_KEY=your_secret_key_here
NEXT_PUBLIC_CLERK_SIGN_IN_URL=/sign-in
NEXT_PUBLIC_CLERK_SIGN_UP_URL=/sign-up
NEXT_PUBLIC_CLERK_AFTER_SIGN_IN_URL=/
NEXT_PUBLIC_CLERK_AFTER_SIGN_UP_URL=/

4. Add ClerkProvider to Layout

// app/layout.tsx
import {
  ClerkProvider,
  SignInButton,
  SignUpButton,
  SignedIn,
  SignedOut,
  UserButton,
} from '@clerk/nextjs'
import type { Metadata } from 'next'

export const metadata: Metadata = {
  title: 'My App',
}

export default function RootLayout({
  children,
}: {
  children: React.ReactNode
}) {
  return (
    <ClerkProvider>
      <html lang="en">
        <body>
          <header className="flex justify-end items-center p-4 gap-4 h-16">
            <SignedOut>
              <SignInButton />
              <SignUpButton />
            </SignedOut>
            <SignedIn>
              <UserButton />
            </SignedIn>
          </header>
          {children}
        </body>
      </html>
    </ClerkProvider>
  )
}

5. Run Your App

pnpm dev

Visit http://localhost:3000 and click "Sign Up" to create your first user.

Key Concepts

proxy.ts vs middleware.ts

Next.js 16 (App Router): Use proxy.ts for Clerk middleware
Next.js ≤15: Use middleware.ts with identical code (filename only differs)
Clerk's clerkMiddleware() function is the same regardless of filename
The matcher configuration ensures proper route handling and performance

Protecting Routes

By default, clerkMiddleware() does not protect routes—all are public. Use auth.protect() to require authentication:

// Protect specific route
import { auth } from '@clerk/nextjs/server'

export default async function Page() {
  const { userId } = await auth()

  if (!userId) {
    // Redirect handled by clerkMiddleware
  }

  return <div>Protected content for {userId}</div>
}

Or protect all routes in proxy.ts:

import { clerkMiddleware } from '@clerk/nextjs/server'

export default clerkMiddleware(async (auth, req) => {
  await auth.protect()
})

Environment Variable Validation

Check for required Clerk keys before runtime:

// lib/clerk-config.ts
export function validateClerkEnv() {
  const required = [
    'NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY',
    'CLERK_SECRET_KEY',
  ]

  const missing = required.filter(key => !process.env[key])

  if (missing.length > 0) {
    throw new Error(`Missing required Clerk environment variables: ${missing.join(', ')}`)
  }
}

Accessing User Data

Use Clerk hooks in client components:

// app/components/user-profile.tsx
'use client'

import { useUser } from '@clerk/nextjs'

export function UserProfile() {
  const { user, isLoaded } = useUser()

  if (!isLoaded) return <div>Loading...</div>

  if (!user) return <div>Not signed in</div>

  return (
    <div>
      <h1>{user.fullName}</h1>
      <p>{user.primaryEmailAddress?.emailAddress}</p>
    </div>
  )
}

Or in server components/actions:

// app/actions.ts
'use server'

import { auth, clerkClient } from '@clerk/nextjs/server'

export async function getUserData() {
  const { userId } = await auth()

  if (!userId) {
    throw new Error('Unauthorized')
  }

  const clerk = await clerkClient()
  const user = await clerk.users.getUser(userId)

  return user
}

Migrating from middleware.ts (Next.js 15) to proxy.ts (Next.js 16)

Step-by-Step Migration

Rename the file from middleware.ts to proxy.ts (location remains same: root or /src)
Keep the code identical - No functional changes needed:
```typescript
// Before (middleware.ts)
import { clerkMiddleware } from '@clerk/nextjs/server'
export default clerkMiddleware()
export const config = { ... }

// After (proxy.ts) - Same code
import { clerkMiddleware } from '@clerk/nextjs/server'
export default clerkMiddleware()
export const config = { ... }
```

Update Next.js version:
bash pnpm add next@latest
Verify environment variables are still in .env.local (no changes needed)
Test the migration:
bash pnpm dev

Troubleshooting Migration

If routes aren't protected, ensure proxy.ts is in the correct location (root or /src)
Check that .env.local has all required Clerk keys
Clear .next cache if middleware changes don't take effect: rm -rf .next && pnpm dev
Verify Next.js version is 16.0+: pnpm list next

Building an MCP Server with Clerk

See CLERK_MCP_SERVER_SETUP.md for complete MCP server integration.

Quick MCP Setup Summary

Install MCP dependencies:
bash pnpm add @vercel/mcp-adapter @clerk/mcp-tools
Create MCP route at app/[transport]/route.ts:
```typescript
import { verifyClerkToken } from '@clerk/mcp-tools/next'
import { createMcpHandler, withMcpAuth } from '@vercel/mcp-adapter'
import { auth, clerkClient } from '@clerk/nextjs/server'

const clerk = await clerkClient()

const handler = createMcpHandler((server) => {
server.tool(
'get-clerk-user-data',
'Gets data about the Clerk user that authorized this request',
{},
async (_, { authInfo }) => {
const userId = authInfo!.extra!.userId! as string
const userData = await clerk.users.getUser(userId)
return {
content: [{ type: 'text', text: JSON.stringify(userData) }],
}
},
)
})

const authHandler = withMcpAuth(
handler,
async (_, token) => {
const clerkAuth = await auth({ acceptsToken: 'oauth_token' })
return verifyClerkToken(clerkAuth, token)
},
{
required: true,
resourceMetadataPath: '/.well-known/oauth-protected-resource/mcp',
},
)

export { authHandler as GET, authHandler as POST }
```

Expose OAuth metadata endpoints (see references for complete setup)
Update proxy.ts to exclude .well-known endpoints:
```typescript
import { clerkMiddleware, createRouteMatcher } from '@clerk/nextjs/server'

const isPublicRoute = createRouteMatcher([
'/.well-known/oauth-authorization-server(.)',
'/.well-known/oauth-protected-resource(.)',
])

export default clerkMiddleware(async (auth, req) => {
if (isPublicRoute(req)) return
await auth.protect()
})
```

Enable Dynamic Client Registration in Clerk Dashboard

Best Practices

1. Environment Variable Management

Always use .env.local for development (never commit sensitive keys)
Validate environment variables on application startup
Use NEXT_PUBLIC_ prefix ONLY for non-sensitive keys that are safe to expose
For production, set environment variables in your deployment platform (Vercel, etc.)

2. Route Protection Strategies

// Option A: Protect all routes
export default clerkMiddleware(async (auth, req) => {
  await auth.protect()
})

// Option B: Protect specific routes
import { createRouteMatcher } from '@clerk/nextjs/server'

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

export default clerkMiddleware(async (auth, req) => {
  if (isProtectedRoute(req)) {
    await auth.protect()
  }
})

// Option C: Public routes with opt-in protection
const isPublicRoute = createRouteMatcher(['/sign-in(.*)', '/sign-up(.*)'])

export default clerkMiddleware(async (auth, req) => {
  if (!isPublicRoute(req)) {
    await auth.protect()
  }
})

3. MCP Server Security

Enable Dynamic Client Registration in Clerk Dashboard
Keep .well-known endpoints public but protect all MCP tools with OAuth
Use acceptsToken: 'oauth_token' in auth() to require machine tokens
OAuth tokens are free during public beta (pricing TBD)
Always verify tokens with verifyClerkToken() before exposing user data

4. Performance & Caching

Use clerkClient() for server-side user queries (cached automatically)
Leverage React Server Components for secure user data access
Cache user data when possible to reduce API calls
Use @clerk/nextjs hooks only in Client Components ('use client')

5. Production Deployment

Set all environment variables in your deployment platform
Use Clerk's production instance keys (not development keys)
Test authentication flow in staging environment before production
Monitor Clerk Dashboard for authentication errors
Keep @clerk/nextjs updated: pnpm update @clerk/nextjs

Troubleshooting

Issues & Solutions

Issue	Solution
"Missing environment variables"	Ensure `.env.local` has `NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY` and `CLERK_SECRET_KEY`
Middleware not protecting routes	Verify `proxy.ts` is in root or `/src` directory, not in `app/`
Sign-in/sign-up pages not working	Check `NEXT_PUBLIC_CLERK_SIGN_IN_URL` and `NEXT_PUBLIC_CLERK_SIGN_UP_URL` in `.env.local`
User data returns null	Ensure user is authenticated: check `userId` is not null before calling `getUser()`
MCP server OAuth fails	Enable Dynamic Client Registration in Clerk Dashboard OAuth Applications
Changes not taking effect	Clear `.next` cache: `rm -rf .next` and restart `pnpm dev`
"proxy.ts" not recognized	Verify Next.js version is 16.0+: `pnpm list next`

Common Next.js 16 Gotchas

File naming: Must be proxy.ts (not middleware.ts) for Next.js 16
Location: Place proxy.ts at project root or in /src directory, NOT in app/
Re-exports: Config object must be exported from proxy.ts for matcher to work
Async operations: clerkMiddleware() is async-ready; use await auth.protect() for route protection

Debug Mode

Enable debug logging:

// proxy.ts
import { clerkMiddleware } from '@clerk/nextjs/server'

export default clerkMiddleware((auth, req) => {
  if (process.env.DEBUG_CLERK) {
    console.log('Request URL:', req.nextUrl.pathname)
    console.log('User ID:', auth.sessionClaims?.sub)
  }
})

Run with debug:

DEBUG_CLERK=1 pnpm dev

mcp-server-skills: General MCP server patterns with Vercel adapter
nextjs16-skills: Next.js 16 features, breaking changes, and best practices
authjs-skills: Alternative authentication using Auth.js (Auth0, GitHub, etc.)

Resources

# Supported AI Coding Agents

This skill is compatible with the SKILL.md standard and works with all major AI coding agents:

⚡ Amp 🚀 Antigravity 🤖 Claude Code 🦀 Clawdbot 📝 Codex ▶️ Cursor 🤖 Droid 💎 Gemini CLI 🐙 GitHub Copilot 🪿 Goose 📊 Kilo Code 🔧 Kiro CLI 💻 OpenCode 🦘 Roo Code 🌲 Trae 🏄 Windsurf

Learn more about the SKILL.md standard and how to use these skills with your preferred AI coding agent.