Cal.com is an open-source scheduling platform designed as a fully customizable, self-hostable alternative to Calendly. Built with the T3 stack (Next.js, tRPC, Tailwind CSS, Prisma, and PostgreSQL), it empowers individuals and organizations to own their scheduling data, workflows, and user interface without vendor lock-in. Whether you’re a solo practitioner managing client appointments or a team deploying branded scheduling across multiple departments, Cal.com provides the flexibility to customize event types, integrations, and appearance while maintaining full control over data privacy and hosting infrastructure.
The project was born out of frustration with the limitations of commercial scheduling tools—lack of customization, opaque data policies, and inflexible pricing. Cal.com addresses these by offering a complete stack that can be deployed on-premises or via cloud providers, with full API access for integration into existing systems. It’s used by developers, small businesses, educators, and enterprises seeking to embed scheduling into their own domains with white-label branding and compliance-ready data handling.
What You Get
- Self-hosted scheduling - Deploy Cal.com on your own infrastructure using Docker or manual setup, giving you full control over data storage, access, and backups without relying on third-party services.
- White-label branding - Customize the look and feel of your scheduling pages with your own domain, logo, colors, and branding—ideal for agencies, SaaS platforms, or enterprises maintaining brand consistency.
- Multi-user roles and permissions - Manage access with built-in roles (Free, Pro, Trial, Admin) and seed test users for development; control who can create events, manage teams, or view analytics.
- tRPC + Next.js backend - Leverage end-to-end type safety with tRPC for API calls and server-side logic, ensuring robust client-server communication without boilerplate code.
- Integrated calendar sync - Connect with Google Calendar, Outlook, and other providers to automatically sync events and avoid double bookings across platforms.
- Real-time availability with Daily.co - Embed video conferencing directly into scheduled events using Daily.co integration, enabling seamless transitions from booking to call.
- Prisma ORM with PostgreSQL - Use a modern, type-safe database layer for managing events, users, and integrations with full migration support and schema validation.
- Dockerized development environment - Spin up a local instance with test data using
yarn dx, including pre-seeded users and a PostgreSQL container, eliminating setup friction for contributors.
- API-driven architecture - Expose scheduling functionality via a programmable API to integrate with CRM systems, custom dashboards, or automated workflows.
Common Use Cases
- Building a branded scheduling portal for clients - A coaching business uses Cal.com to host its booking page on their domain (book.mycoachingbusiness.com) with custom branding, syncs to Google Calendar, and embeds Zoom links—all without paying monthly SaaS fees.
- Developing a multi-tenant SaaS product with embedded scheduling - A startup builds a platform where each customer gets their own branded Cal.com instance via API, allowing users to schedule calls without leaving the host app.
- Problem: Vendor lock-in with Calendly → Solution: Self-hosted alternative - Teams tired of Calendly’s limited customization, hidden costs, and data restrictions switch to Cal.com to control their event data, add custom fields, and avoid per-user pricing.
- DevOps teams managing internal tooling - Engineering teams deploy Cal.com internally to streamline meeting scheduling across departments, integrating with Slack and corporate directories while maintaining compliance with data residency policies.
Under The Hood
Cal.com is a comprehensive open-source scheduling platform designed to offer flexible, extensible solutions for calendar management and meeting coordination. It emphasizes developer experience, modular architecture, and enterprise-grade customization through a combination of modern frameworks and thoughtful design patterns.
Architecture
The system adopts a monolithic structure with well-defined modules and layered organization, promoting separation of concerns through feature-based grouping. It implements key design patterns such as repository, factory, and dependency injection to manage complexity and support scalability.
- Clear module organization with feature-based grouping and strong separation of concerns
- Extensive use of design patterns to manage complexity and enhance maintainability
- Integration points between core features like organization creation and user permissions
- Emphasis on structured business logic through agent-based architecture and vertical slices
Tech Stack
The platform is built using TypeScript, leveraging React and Next.js for a modern full-stack development experience. It integrates a rich ecosystem of tools to support type safety, testing, and scalable architecture.
- Built with TypeScript, React, and Next.js for robust frontend and backend development
- Relies on Prisma for database operations, TRPC for API handling, and Zod for schema validation
- Utilizes TurboRepo for monorepo management and Vitest/Playwright for testing
- Employs Biome for code formatting and linting to maintain consistency
Code Quality
The codebase demonstrates a mature testing strategy with extensive coverage across integration and end-to-end scenarios. It enforces consistent naming and architectural patterns while managing technical debt in legacy components.
- Comprehensive test suite covering unit, integration, and end-to-end scenarios
- Structured error handling with clear propagation of domain-specific issues
- Consistent naming and architectural patterns across modules
- Moderate technical debt in legacy middleware and conditional logic structures
What Makes It Unique
Cal.com distinguishes itself through its innovative agent-based architecture and focus on extensibility, offering a unique blend of open-source flexibility and enterprise-grade customization. Its approach to localization and modular design sets it apart in the scheduling space.
- Agent-based architecture for managing business logic and development practices
- Sophisticated i18n and localization support tailored for global use cases
- Modular vertical slice architecture that enables customization and feature flags
- Strong emphasis on developer experience with structured rules and automation