> For the complete documentation index, see [llms.txt](https://llm-aws.course.gspivey.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://llm-aws.course.gspivey.com/foundations/introduction-to-apis/what-is-curl.md).

# What is cURL?

`cURL` (client URL) is a command-line tool for transferring data to and from a server. It supports HTTP, HTTPS, and many other protocols, and runs on almost every platform. This makes cURL ideal for testing API communication from any device with a command line and network connectivity.

The most basic command is `curl [URL]`. The `curl` command followed by a URL retrieves the resource at that address — for a web page, it returns the HTML source.

To use cURL with REST APIs, you specify different HTTP methods along with headers and data. Here are common examples:

1. **GET Request** — retrieve data from the server:

   ```
   curl http://api.example.com/resource
   ```
2. **POST Request** — send data to the server (JSON in this case):

   ```
   curl -X POST -H "Content-Type: application/json" -d '{"key":"value"}' http://api.example.com/resource
   ```
3. **PUT Request** — update existing data on the server:

   ```
   curl -X PUT -H "Content-Type: application/json" -d '{"key":"value"}' http://api.example.com/resource/id
   ```
4. **DELETE Request** — delete existing data from the server:

   ```
   curl -X DELETE http://api.example.com/resource/id
   ```

In these examples, `-X` specifies the HTTP method, `-H` sets request headers, and `-d` sends data in the request body.

The actual commands vary based on the API's specifications. Always refer to the API documentation for accurate request formats.

### Key cURL Resources

* The Tutorial from the official cURL website
  * <https://curl.se/docs/tutorial.html>
* The open source cURL book from the Everything cURL website
  * <https://everything.curl.dev/index.html>