Using curl to test a web API is a common practice among developers, as it provides a quick and flexible way to send HTTP requests from the command line. curl is a command-line tool available on most Unix-based systems (including Linux and macOS) and Windows, used to transfer data to or from a server. It supports various protocols, including HTTP, HTTPS, FTP, and more.

Here’s a guide on how to use curl for testing a web API:

1. Basic GET Request

To send a GET request to an API endpoint, you would use curl followed by the URL. For example:


This command retrieves data from the specified URL.

2. Including Headers

Often, you need to include headers in your request. For instance, to include an Authorization header for a token or to specify the content type, use the -H option:

curl -H "Authorization: Bearer YOUR_TOKEN" -H "Content-Type:application/json"

3. POST Request with Data

To send data to the server, such as creating a new record via a POST request, use the -d option to include the data payload:

curl -X POST -H "Content-Type: application/json" -d '{"name":"John", "age":30}'

This sends a JSON payload to the server.

4. PUT and DELETE Requests

Similarly, for PUT (update) and DELETE requests, specify the method with -X:

# PUT request 
curl -X PUT -H "Content-Type: application/json" -d '{"name":"John",  "age":31}' 

# DELETE request 
curl -X DELETE

5. Handling Cookies

If you need to send or receive cookies, use the -b option to send cookies and -c to store the cookies returned from the server:

# Send cookies 
curl -b "name=value" 

# Store cookies 
curl -c cookies.txt

6. Verbose and Debugging

For debugging, the -v (verbose) option is useful as it displays the request and response headers:

curl -v

7. Saving Response to a File

To save the response to a file, use the -o option:

curl -o output.txt

8. Using Secure Connections

For secure connections (HTTPS), curl automatically uses SSL. You can specify SSL options with --ssl, though in most cases, curl handles SSL without extra input.

9. Timeouts

For setting timeouts, use the --connect-timeout option to specify the maximum time allowed for the connection to the server:

curl --connect-timeout 10

10. Following Redirects

If the API might redirect, use -L to tell curl to follow redirects:

curl -L


curl is a powerful tool for testing web APIs. It allows you to quickly send various types of requests, inspect responses, and interact with APIs in a straightforward manner.

As a command-line tool, it’s also convenient for automating tests and integrating into scripts.

You can download curl for just about every operating system from here: –


Hi, my name is Stephen Finchett. I have been a software engineer for over 30 years and worked on complex, business critical, multi-user systems for all of my career. For the last 15 years, I have been concentrating on web based solutions using the Microsoft Stack including ASP.Net, C#, TypeScript, SQL Server and running everything at scale within Kubernetes.