Clerk

Authentication and user management platform for web and mobile applications. Delivers drop-in components for sign-up, sign-in, and user profile flows while handling session management, multi-factor auth, and social logins behind a single SDK.

Used by teams at Notion, Linear, and thousands of production apps. Clerk stands out by combining a hosted backend with embeddable UI components that developers customize via props or themes, avoiding the choice between building auth from scratch or locking into rigid hosted login pages.

Key capabilities:

• Prebuilt React, Next.js, and vanilla components with customization options
• Social providers, email magic links, and passkey support
• Organizations, roles, and permissions for B2B apps
• Webhook-driven user lifecycle events for downstream systems
• Session and token management with JWTs and rotation

Developers adopt Clerk to ship auth quickly while retaining control over UX. Backend integration happens via middleware or SDK, and user data syncs to existing databases or stays in Clerk for a fully managed model.