cURL is a general-purpose command-line tool for interacting with REST APIs. Using cURL to submit a single request at the command line is a common method of experimenting with an API before deciding whether to write software to automate that request. The Rackspace API documentation includes many cURL-based examples.
The following Rackspace publications provide basic information about cURL:
In the Developer Center, you can see examples of using cURL to send requests to the API endpoints for many Rackspace cloud services. Select a service, and then click SHELL as your preferred language to see samples formatted for use at the command line with cURL.
You can use any tool that enables you to type a command, send it as a request to a REST API's endpoint, and then examine the API's response.