Clerk
Drop-in auth with pre-built UI components — sign-up, sign-in, and user management in minutes
Clerk gives you a complete auth system without building one. Install the package, drop in the sign-up component, and you have Google login, email/password, MFA, and user profiles working. The UI components look professional without any styling work.
The 10,000 MAU free tier is genuinely generous — most early startups will not outgrow it for months. The concern is lock-in: once your app is wired to Clerk’s components and APIs, moving to something else is a significant rewrite. If you are validating an idea and need auth fast, Clerk is the fastest path. If you are building something you expect to maintain for years, consider whether the convenience is worth the dependency.
What's good
- Pre-built React components for auth that actually look good out of the box
- 10,000 monthly active users free — most startups run free for months
- Handles the hard stuff: MFA, social login, organization management
Watch out for
- Vendor lock-in is real — migrating away from Clerk means rebuilding auth
- Pricing jumps at scale (10k+ MAU) can surprise you
- React-focused — less polished for non-React stacks
Alternatives
More in Authentication
Auth0
Enterprise-grade auth that handles every login method — from social login to SAML SSO
Firebase Auth
Google's authentication service with generous free limits and tight integration across the Firebase ecosystem
Lucia
Lightweight open-source auth library that gives you full control over your authentication logic