# Getting Started with cURL As a developer, whatever we code eventually gets deployed on a **server**. A server is nothing but a program that runs somewhere and serves our application to users. Users usually interact with this server through a **browser**. The browser sends requests to the server and shows the response in a user-friendly way. But as developers, we often want to test backend changes **without a UI**. Testing APIs or backend logic only through a browser is either impossible or very inconvenient. This is where **cURL** comes in. --- ## What is cURL? cURL is a **command-line tool** that allows us to make requests to a server. In simple terms: > cURL lets you send messages to a server directly from the terminal. It is very useful for developers because: * It helps in **testing backend APIs** * It helps in **troubleshooting server issues** * It allows testing functionality **independent of the UI** cURL supports multiple protocols, but in this article we will focus only on **HTTP / HTTPS**. Even though it might look complex or scary because it’s a CLI tool, it is actually **quite simple to use**. --- ## Making Your First Request Using cURL Let’s start with the most basic example: Fetching a webpage from a locally running **nginx server**. ```plaintext root@db997926b412:/# curl localhost Welcome to nginx!

Welcome to nginx!

If you see this page, the nginx web server is successfully installed and working. Further configuration is required.

For online documentation and support please refer to nginx.org.
Commercial support is available at nginx.com.

Thank you for using nginx.

``` Here, cURL fetched the **raw HTML** from the server. If we open the same URL in a browser, we see a nicely rendered page. The content is the same - the difference is that the **browser knows how to render HTML**, while cURL just prints it as text. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1769874794525/aeefab1a-a545-4b87-80e5-10a6063d4cf3.png align="center") ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1769874826093/24c2ed24-84c6-4721-bf34-ce99311fa123.png align="center") --- ## Understanding the Response (Headers and Body) To see more details about what’s happening behind the scenes, we can ask cURL to show a **verbose response**. ```plaintext curl -v localhost ``` ```plaintext * Trying 127.0.0.1:80... * Connected to localhost (127.0.0.1) port 80 (#0) > GET / HTTP/1.1 > Host: localhost > User-Agent: curl/7.88.1 > Accept: */* > < HTTP/1.1 200 OK < Server: nginx/1.27.5 < Date: Sat, 31 Jan 2026 14:55:07 GMT < Content-Type: text/html < Content-Length: 615 < Last-Modified: Wed, 16 Apr 2025 12:01:11 GMT < Connection: keep-alive < ETag: "67ff9c07-267" < Accept-Ranges: bytes < ... ``` From this output we can clearly see: * The **request** being sent (`GET /`) * The **response status** (`200 OK`) * The **headers** sent by the server * The **response body** (HTML content) --- ## What Happens When a Page Doesn’t Exist? If we try to access a path that doesn’t exist, the server responds with an error. ```plaintext curl -v localhost/path ``` ```plaintext < HTTP/1.1 404 Not Found < Server: nginx/1.27.5 ... ``` This shows a **404 error**, meaning the requested resource was not found. All the requests we made so far were **GET requests**, which we can also confirm from the request headers. --- ## Using cURL to Talk to APIs cURL is not limited to fetching web pages. It is commonly used to test **APIs**. Below is an example of using cURL to test a **POST API** for user registration. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1769874885541/51faa147-e59b-416f-b91f-79c1027cb4cf.png align="center") The response shows a **200 status code**, which means the request was successful. Next, we try logging in using the newly created user. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1769874904900/7963b2e7-e24c-4918-a5f7-3516f7f1d14e.png align="center") The login also works successfully. Now let’s try passing **invalid credentials**. ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1769874914188/3cb5346b-314d-4820-b680-85d903480ae7.png align="center") This time, the API responds with an error, which confirms that we are properly testing different scenarios. Using cURL, we are able to test APIs **directly from the terminal**, without needing any UI. --- ## Basic cURL Flags Used In the API examples above, we used a few common cURL flags. Let’s understand them: * `--url` Tells cURL the URL to which the request should be sent. * `--request` Specifies the HTTP method to use (for example, POST). * `--header` Used to pass headers along with the request. Multiple headers can be passed by using this flag multiple times. * `--data` Used to send the request body or payload expected by the API. There are many more flags and ways to use cURL, but this article focuses only on the **basics** needed to get started.