Clerk

Clerk is a developer-first authentication and user management platform founded in 2019 by Colin Sidoti and Shaw Tesoro, backed by Y Combinator and over thirty million dollars in funding from investors including Stripe and Meritech, providing pre-built, customizable authentication components including sign-in, sign-up, user profile, and organization management screens that integrate in minutes with React, Next.js, and other JavaScript frameworks, adopted by companies including Vercel, Resend, Dub, and Cal.com for managing user identity. The pre-built UI components provide production-ready sign-in and sign-up flows with email and password, passwordless email links, OAuth social login with Google, GitHub, Apple, Facebook, Microsoft, and dozens of other providers, multi-factor authentication through TOTP authenticator apps and SMS codes, and passkey support for passwordless WebAuthn authentication, all customizable through CSS variables, custom pages, or complete component replacement. The user management provides a comprehensive dashboard for administrators to view, search, filter, and manage users, with user metadata, custom attributes, ban and suspension capabilities, impersonation for support, and bulk operations. The organization and B2B support enables multi-tenant applications with organizations, roles, invitations, and member management, with organization-level SAML SSO and SCIM provisioning for enterprise customers. The session management uses JWT-based sessions with configurable token lifetimes, refresh tokens, and session revocation, with server-side session validation through backend SDKs. The webhooks notify external systems of user lifecycle events. The BYOK feature allows using your own authentication keys. Designed for frontend developers, full-stack teams, and SaaS startups.