Caddy is an open-source, extensible web server written in Go, designed to simplify how websites, services, and applications are deployed and served. It is widely used as an HTTP server and reverse proxy, but its modular architecture allows it to function as a broader platform for running long-lived services.

One of Caddy’s defining features is its automatic HTTPS capability. It was the first major web server to enable HTTPS by default, automatically obtaining and renewing TLS certificates without requiring manual configuration. This removes the complexity typically associated with certificate management and improves security by default.

Caddy uses a flexible configuration system that can be defined through a simple configuration file (Caddyfile), JSON, or dynamically via a REST API. This allows developers to manage server behavior programmatically or declaratively, making it suitable for both simple setups and large-scale deployments.

The server supports modern web standards including HTTP/1.1, HTTP/2, and HTTP/3, and includes built-in features such as load balancing, reverse proxying, static file serving, and observability. Its modular plugin system allows developers to extend functionality by adding custom modules compiled into the binary.

Caddy is designed to be easy to deploy, with a single static binary and no runtime dependencies, and can run across major operating systems and environments including containers and Kubernetes. It is positioned as a simpler, more secure alternative to traditional web servers like Nginx or Apache.

Key features include:

• Automatic HTTPS with certificate issuance and renewal
• Built-in reverse proxy, load balancing, and static file server
• Support for HTTP/1.1, HTTP/2, and HTTP/3
• Flexible configuration via Caddyfile, JSON, or API
• Modular architecture with plugin extensibility
• Cross-platform with a single binary and no dependencies

Common use cases include:

• Hosting websites
• Serving static files
• Running reverse proxies for backend services
• Managing TLS certificates automatically
• Deploying SaaS platforms,
• Building scalable web infrastructure

Caddy was created by Matthew Holt and is developed as an open-source project with contributions from a global community. It is maintained under the caddyserver organization and supported by sponsors and contributors.