cURL is a popular command-line tool for transferring data with URLs. It is compatible with many protocols and can be used by any terminal installed with libcurl, cURL's client-side URL request library. Due to its ubiquity, cURL is a common method for developers to test API request behaviors. cURL was originally developed by Daniel Stenberg and released in 1997 for an IRC scenario. It is now maintained by an active open community of developers.