Clerk

Clerk sells authentication as embeddable UI: <SignIn/> and <UserProfile/> components plus flexible APIs and an admin dashboard that handle sign-up, session management, MFA, social and enterprise login, and user data. Founded in 2019 by brothers Colin and Braden Sidoti, the company differentiated from API-first auth vendors by leading with polished components that set a new bar for auth UX.

In January 2024 Clerk raised a $30M Series B led by CRV with participation from Stripe, bringing total funding to $55.5M. At the raise the company reported growing from 1M to over 16M managed users and 1,300+ paying customers across SaaS, AI, fintech, and e-commerce, with more than one sign-up per second. The Stripe investment marked a strategic partnership to expand from authentication into authorization, tying Stripe Billing plans to feature entitlements without webhooks.

For AI app builders, Clerk is the default choice in the Next.js ecosystem: it plugs into the App Router in minutes and its organization model maps cleanly onto team-based agent products. Pricing starts free up to 10,000 MAU, then $25/month. The authorization layer is still newer than the auth core, so teams with complex permission models should evaluate it against dedicated PDPs.

Sign up at clerk.com, install the SDK for your framework, add the middleware and components.