What is cURL? A Complete Guide to Commands & Testing

cURL is one of those tools every developer bumps into sooner or later — API testing, network debugging, automation, CI scripts. This guide covers what it is, the options you’ll actually use, and how to turn a one-off cURL command into an organized, reusable request in Requestly.

What is cURL?

cURL (Client URL) is a free, open-source command-line tool and library for transferring data using a wide range of network protocols, including HTTP, HTTPS, FTP, SFTP and more. Because it’s scriptable and available almost everywhere, cURL has become the lingua franca for describing an HTTP request.

How cURL is commonly used

• API testing & development — hit an endpoint and read the raw response
• Downloading files — pull assets or artifacts in scripts
• Webhooks & automation — trigger and verify callbacks
• Health checks & monitoring — quick uptime and status probes

How to create cURL requests

A basic GET request:

curl https://api.example.com/users

A POST with a JSON body:

curl -X POST https://api.example.com/users \
     -H "Content-Type: application/json" \
     -d '{"name":"John Doe","email":"john@example.com"}'

How to import a cURL request into Requestly

Once a cURL command grows past a couple of flags, the terminal stops being a great place to live. In Requestly, choose Import → cURL, paste the command, and it becomes a fully editable request — method, headers, body and auth — saved in a collection and versioned in your Git.