libcurl

libcurl is a free and open-source client-side URL transfer library. Written in C, it provides a portable, efficient interface for transferring data with URLs. The library is used to implement network transfer functionality in applications and serves as the foundation for the curl command-line tool.

libcurl supports a wide range of protocols, including HTTP, HTTPS, FTP, FTPS, SCP, SFTP, LDAP, SMTP/IMAP/POP3, RTSP, RTMP, and FILE. It offers authentication, cookies, proxies, TLS/SSL, client certificates, redirects, resume of transfers, HTTP/2, and parallel transfers via its multi interface.

The library provides an easy interface (CURL *easy) and a multi interface for parallel transfers, plus a share interface for reusing data. It is designed to be portable and used from many languages via bindings. The curl command-line tool also relies on libcurl.

libcurl was created by Daniel Stenberg in 1997 and has since been maintained by the curl project with contributions from volunteers. It is released under a permissive license, commonly described as MIT-style or curl license.