Clerk

Clerk handles sign-in, sign-up and user management with prebuilt components for React and Next.js. You get email, social login, passkeys, multi-factor and organization support without writing the screens yourself.

Developers like the polished UI and the generous free tier, which is why many AI-built starter projects use it. Webhooks and a dashboard make it easy to see who is signing up.

Pricing is per monthly active user, so costs rise with success. For most startups the time saved on auth is worth it.