curl

curl is a command-line tool and library for transferring data with URL syntax, supporting over 25 protocols including HTTP, HTTPS, HTTP/2, HTTP/3 (QUIC), FTP, FTPS, SFTP, SCP, TFTP, LDAP, LDAPS, DICT, TELNET, FILE, IMAP, IMAPS, POP3, POP3S, SMTP, SMTPS, RTSP, RTMP, MQTT, SMB, SMBS, GOPHER, and WebSocket. Created in 1998 by Daniel Stenberg (who remains the lead maintainer), curl has become the most widely used HTTP client in the world: it is installed by default on macOS, most Linux distributions, and Windows 10+, and the libcurl library powers HTTP communication in thousands of applications including cars, televisions, routers, and spacecraft. As of 2026, curl has over 36,000 stars and is downloaded billions of times annually. Key curl features include: HTTP methods (GET, POST, PUT, DELETE, PATCH, HEAD, OPTIONS, CONNECT), authentication (Basic, Bearer, Digest, NTLM, Negotiate/SPNEGO, AWS Signature v4), cookie handling (-b for sending, -c for saving), custom headers (-H), POST data from strings, files, or @file syntax, form data upload (-F for multipart/form-data), JSON API testing (--json), resumable downloads with range requests (-C -), progress bars (--progress-bar), parallel transfers (--parallel), retry logic (--retry N with backoff), proxy support (HTTP, HTTPS, SOCKS4, SOCKS5), SSL/TLS options (--insecure, certificate pinning via --pinnedpubkey), HTTP/2 and HTTP/3 multiplexing, connection pooling, output to file (-o) or stdout, write callback for custom data handling, and verbose debugging (-v). libcurl provides the same functionality as a C library with bindings for 60+ languages.