cURL (pronounced 'curl'[4]) is a computer software project providing a library (libcurl) and command-line tool (curl) for transferring data using various protocols. It was first released in 1997.[5] The name stands for "Client URL".[6] The original author and lead developer is the Swedish developer Daniel Stenberg.[1]

Example output from curl -O
Original author(s)Daniel Stenberg[1]
Developer(s)Contributors to the cURL project
Initial release1997 (1997)[2]
Stable release7.67.0 (6 November 2019 (2019-11-06)[3]) [±]
Written inC
Operating systemAIX, AmigaOS, BeOS, Chrome NaCl, DOS, DragonFly BSD, FreeBSD, GNU-Darwin, HPUX, Haiku, Hurd, IRIX, Linux, macOS, MiNT, Midnight BSD, Minix, NetBSD, NetWare, Nexenta, OS/2, Open Server, OpenBSD, Plan9, QNX, RISC OS, Solaris, Syllable, Tru64 UNIX, UnixWare, VMS, Microsoft Windows, z/OS
TypeFTP client / HTTP client
LicenseFree Software: MIT/X derivate license


libcurl is a free client-side URL transfer library,[7] supporting cookies, DICT, FTP, FTPS, Gopher, HTTP/1[8] (with HTTP/2 support), HTTP POST, HTTP PUT, HTTP proxy tunneling, HTTPS, IMAP, Kerberos, LDAP, POP3, RTSP, SCP, and SMTP. 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.

The libcurl library is portable. It builds and works identically on many platforms, including AIX, AmigaOS, Android, BeOS, BlackBerry Tablet OS and BlackBerry 10,[9] 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, and Microsoft Windows.[10]

The libcurl library is free, thread-safe and IPv6 compatible. Bindings are available for more than 40 languages, including C/C++, Java, PHP and Python.

The libcurl library can support axTLS,[11] GnuTLS, mbed TLS, NSS, QSOSSL on IBM i, SChannel on Windows, Secure Transport on macOS and iOS, SSL/TLS through OpenSSL, and wolfSSL.


cURL is a command-line tool for getting or sending data including files using URL syntax.

Since cURL uses libcurl, it supports a range of common network protocols, currently including HTTP,[8][12] HTTPS, SOAP requests,[12] FTP, FTPS, SCP, SFTP, TFTP, LDAP, DAP, DICT, TELNET, FILE, IMAP, POP3, SMTP and RTSP (the last four only in versions newer than 7.20.0 or 9 February 2010).

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.[13]

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.


Basic use of cURL involves simply typing curl at the command line, followed by the URL of the output to retrieve:


cURL defaults to displaying the output it retrieves to the standard output specified on the system (usually the terminal window). So running the command above would, on most systems, display the source-code in the terminal window. The -o flag can be used to store the output in a file instead:

   curl -o example.html

More options that change the tool's behavior are available.

See also

  • 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 akin to curl
  • Web crawler – an internet bot that can crawl the web
  • Wget – similar command-line tool with no associated library but capable of recursive downloading


  1. Stenberg, Daniel (20 March 2015). "curl, 17 years old today". Retrieved 20 March 2015.
  2. "History of curl - How curl Became Like This". curl. Archived from the original on September 30, 2017. Retrieved November 17, 2016. Daniel simply adopted an existing command-line open-source tool, httpget, that Brazilian Rafael Sagula had written and recently release version 0.1 of. After a few minor adjustments, it did just what he needed. [] HttpGet 1.0 was released on April 8th 1997 with brand new HTTP proxy support.
  3. "curl – Changes". cURL. Retrieved 7 November 2019.
  4. cURL - Frequently Asked Questions
  5. "cURL: docs/ | Fossies". Retrieved September 29, 2019.
  6. Stenberg, Daniel. "Origin of the name". Retrieved 2018-04-25.
  7. Jones, M. Tim (8 September 2009). "Conversing through the Internet with cURL and libcurl - Using libcurl with C and Python". IBM Developerworks. Archived from the original on 14 April 2015. Retrieved 12 September 2018.
  8. Stenberg, Daniel (5 August 2019). "http09: disable HTTP/0.9 by default in both tool and library". GitHub. Archived from the original (html) on 5 August 2019. Retrieved 5 August 2019. As the plan has been laid out in DEPRECATED. Update docs accordingly and verify in test 1174.
  9. "Open Source Components for the Native SDK for BlackBerry Tablet OS". Archived from the original on 2013-01-27. Retrieved 2017-09-19.
  11. axTLS
  12. "Hello World with cURL" (html). Cisco DevNet. Retrieved 29 September 2019. cURL can be used, among other things, to make HTTP requests, including SOAP requests.
  13. cURL - Protocol docs - SSL Certificate Verification
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