Curl is a command-line tool and portable library for transferring data across a wide range of network protocols. It functions as a unified engine that abstracts diverse communication standards, allowing users and developers to move files and information between servers using a consistent interface. The project provides both a versatile command-line client for terminal-based automation and a stable programmatic interface for integrating complex network operations into applications.
The system is distinguished by its protocol-agnostic core and its ability to manage both synchronous and asynchronous network transfers. It features a non-blocking event loop that enables multiple simultaneous transfers within a single thread, alongside a connection pooling mechanism that reuses network sockets to minimize latency. Security is a primary focus, implemented through a pluggable architecture that supports various cryptographic backends, native certificate store integration, and comprehensive authentication mechanisms for protected resources.
Beyond core data movement, the project includes extensive support for modern networking standards, including HTTP/3, WebSockets, and MQTT. It offers sophisticated state management through a built-in cookie engine and provides granular control over request headers, URL construction, and batch processing. These capabilities are supported by robust debugging tools that allow for the inspection of raw request and response data during development.
The project is distributed with standard configuration scripts and package management support to facilitate integration into diverse build environments.