Before diving into cURL, let’s first understand the basics.
What Is a Server and Why Do We Talk to It?
When you open a website or use an app, your device is not doing all the work.
It asks another computer on the internet to send data. That computer is called a server.
Examples:
When you open Google → your browser talks to Google’s server
When your app shows products → it talks to an API server
When you submit a form → data is sent to a server
So every time something loads from the internet, this is happening:
Client → sends request → Server → sends response
Where Does cURL Fit In?
Usually, the client is:
But sometimes developers want to talk to the server directly, without any UI.
That is where cURL comes in.
cURL is a tool that lets you send requests to a server from the terminal and see the raw response.
Think of it as:
A browser for developers, inside the terminal.
You type a command, the request is sent, and the server sends back data.
cURL
What Is cURL
cURL is a command-line tool used to send and receive data using URLs.
It can:
Request web pages
Talk to APIs
Send data to servers
Download files
But instead of clicking buttons, you type commands.
Why we need cURL
Developers use cURL because:
You can test if a server is working
You can test APIs without writing frontend code
You can debug request and response behavior
It works almost everywhere (Linux, macOS, Windows)
It is often the first tool used to check backend systems.
First Request Using cURL
Let’s start with the simplest possible example.
curl https://jsonplaceholder.typicode.com/todos/1
This command:
Sends a request to the server
The server sends back data
cURL prints that data in the terminal
You will see something like:
This is exactly what a browser would receive, but now you are seeing it directly.
Understanding Request and Response
Every network call has two parts:
Request (What You Send)
It contains:
The URL
The request method (GET, POST, etc.)
Optional data and headers
Example: “Give me todo item number 1.”
Response (What You Get Back)
It contains:
Example:
And then the actual data (HTML, JSON, file, etc.).
cURL shows you the response body by default, which is usually what you care about first.
Using cURL to Talk to server
Most APIs work using HTTP requests.
GET — Asking for Data
GET is used when you want to fetch something.
curl https://jsonplaceholder.typicode.com/posts/1
Meaning: “Give me the post with ID 1.”
POST — Sending Data
POST is used when you want to send new data to the server.
curl -X POST https://jsonplaceholder.typicode.com/posts \
-H "Content-Type: application/json" \
-d '{
"title": "Hello",
"body": "Learning cURL",
"userId": 1
}'
Here:
Meaning: “Create a new post using this data.”
The server may responds with the created object.
Seeing More Details with Verbose Mode
Sometimes you want to see what is happening behind the scenes.
Use:
curl -v https://api.github.com/search/users?q=satpalsinhrana
Verbose mode shows:
Request headers sent
Status code returned
Response headers
It will look something like:
This helps when:
But for normal usage, you usually do not need -v.
Downloading a File Instead of Printing It
By default, cURL prints everything in the terminal.
To save the response into a file:
curl -o google.html https://www.google.com
Now the data is written into google.html instead of the screen.
Following Redirecting Request
Sometimes you type google.com but the server moves you to www.google.com. By default, cURL stops at the redirect. Use -L (Location) to tell cURL to follow the trail to the final destination.
Example of Normal Request
curl google.com
Example of Following Redirecting Request
curl -L google.com
cURL Options
cURL supports many options, but you do not need most of them at the start.
For beginners, these are enough:
| Flag | Meaning | Simple Terms |
-v | Verbose | Show me Very much detail |
-o | Output | Write Output to a file |
-L | Location | Follow the new Location (Redirects) |
-X | Request Method | execute this method (GET/POST) |
-d | Data | Send this Data |
-H | Header | Add this Header |
Fun Time
Try this in your terminal:
curl wttr.in
Or, for a custom ASCII-style response, check out my server:
curl https://ascii.satpal.cloud/
Github Repo 🔗
If you can use cURL comfortably, you already understand how the web really works behind the UI.
“Understanding client and server is the first step to mastering the web.”
— Unknown
To uncover more secrets about the invisible infrastructure powering your daily life, be sure to read my full series on The Internet.
Check out the full series: The Internet by Satpalsinh Rana
