CURL

For other uses, see Curl.

Not to be confused with Curl (programming language).

cURL (pronounced like "curl",^[7] /kɜːrl/) is a free and open source computer program for transferring data to and from Internet servers. It can download a URL from a web server over HTTP, and supports a variety of other network protocols, URI schemes, multiple versions of HTTP, and proxying. The project consists of both a library (libcurl) and command-line tool (curl), which have been widely ported to different computing platforms.

curl

Original author(s)	Daniel Stenberg[1]
Developer(s)	Contributors to the curl project
Initial release	1996; 29 years ago (1996)[2]
Stable release	8.14.1[3]  / 4 June 2025
Repository	github.com/curl/curl
Written in	C
Platform	Cross-platform
Type	web client (supports e.g. HTTPS, and FTP)
License	curl license[4][5] (inspired on the MIT License[5]), also ISC, 3-clause BSD, 4-clause BSD[6]
Website	curl.se

It was created by Daniel Stenberg, who is still the lead developer of the project.

History

The software was first released in 1996,^[8] originally named httpget and then became urlget, before adopting the current name of curl.^[9][10] The name stands for "Client for URL".^[11] The original author and lead developer is the Swedish developer Daniel Stenberg, who created curl to power part of an IRC bot, because he wanted to automatically provide currency exchange rates, fetched from a website, to users in an IRC chat room.^[2]

Components

libcurl

libcurl is a client-side URL transfer library that powers curl,^[12] supporting DICT, FTP, FTPS, Gopher, HTTP/1^[13] (with HTTP/2 and HTTP/3 support), HTTP cookies, HTTP POST, HTTP PUT, HTTP proxy tunneling, HTTPS, IMAP, Kerberos, LDAP, MQTT, POP3, RTSP, RTMP, SCP, SMTP, and SMB. The library supports the file URI scheme, SFTP, Telnet, TFTP, file transfer resume, FTP uploading, HTTP form-based upload, HTTPS certificates, LDAPS, proxies, and user-plus-password authentication.^[14]

The libcurl library is portable, as it builds and works identically on most platforms, including AIX, AmigaOS, Android,^{[citation needed]} BeOS, BlackBerry Tablet OS and BlackBerry 10,^[15] OpenVMS, Darwin, DOS, FreeBSD, HP-UX, HURD, iOS, IRIX, Linux, macOS, NetBSD, NetWare, OpenBSD, OS/2, QNX Neutrino, RISC OS, Solaris, Symbian, Tru64, Ultrix, UnixWare, Microsoft Windows and OpenHarmony.^[16][17][18]

The libcurl library is thread-safe and IPv6 compatible. Bindings are available for more than 50 languages, including C/C++, Java, Julia (is bundled with), PHP and Python.^[19]

The libcurl library supports GnuTLS, mbed TLS, NSS, GSKit on IBM i, SChannel on Windows, Secure Transport on macOS and iOS, SSL/TLS through OpenSSL, BoringSSL, libreSSL, AmiSSL, wolfSSL, BearSSL and rustls.^[20]

curl

curl is a command-line tool for getting or sending data including files using URL syntax. curl provides an interface to the libcurl library; it supports every protocol libcurl supports.^[14]

curl supports HTTPS and performs SSL certificate verification by default when a secure protocol is specified such as HTTPS. When curl connects to a remote server via HTTPS, it will obtain the remote server certificate, then check against its CA certificate store the validity of the remote server to ensure the remote server is the one it claims to be. Some curl packages are bundled with CA certificate store file. There are several options to specify a CA certificate such as --cacert and --capath. The --cacert option can be used to specify the location of the CA certificate store file. In the Windows platform, if a CA certificate file is not specified, curl will look for a CA certificate file name “curl-ca-bundle.crt” in the following order:

1. Directory where the curl program is located.
2. Current working directory.
3. Windows system directory.
4. Windows directory.
5. Directories specified in the %PATH% environment variables.^[21]

curl will return an error message if the remote server is using a self-signed certificate, or if the remote server certificate is not signed by a CA listed in the CA cert file. -k or --insecure option can be used to skip certificate verification. Alternatively, if the remote server is trusted, the remote server CA certificate can be added to the CA certificate store file.

See also

• Free and open-source software portal

• curl-loader – an open-source testing tool based on curl
• libwww – an early library that comes with a command line interface
• PowerShell – the iwr (Invoke-WebRequest) Windows PowerShell had functionality similar to curl; class Web-client too.^[22]
• Web crawler – an internet bot that can crawl the web
• Wget – similar command-line tool with no associated library but capable of recursive downloading