command-line tool and library for transferring data with URLs ,can be used for api testing


CURL, which stands for Client URL, is a command-line tool and library for transferring data with URLs. It is a versatile tool that supports various protocols, including HTTP, HTTPS, FTP, FTPS, SCP, SFTP, LDAP, and more. CURL is widely used for automating tasks that involve making web requests, such as API testing, web scraping, and downloading files from the internet.

As an API automation tool, CURL allows developers and testers to make HTTP requests, validate responses, and automate the interaction with RESTful APIs, making it an essential tool in the development and testing toolkit.


CURL comes packed with a multitude of features that make it a powerful tool for API automation and data transfer:

  1. Support for Multiple Protocols: CURL supports a wide variety of protocols including HTTP, HTTPS, FTP, FTPS, SCP, SFTP, LDAP, and more, making it highly versatile.
  2. HTTP Methods: It supports all standard HTTP methods such as GET, POST, PUT, DELETE, OPTIONS, HEAD, PATCH, etc., which are essential for interacting with RESTful APIs.
  3. Custom Headers: Users can add custom headers to their requests, allowing for testing of specific scenarios and API behaviors.
  4. Data Upload and Download: CURL can handle file uploads and downloads, supporting various data formats and transfer methods.
  5. Authentication Support: It supports various authentication methods, including Basic Auth, Digest, NTLM, Negotiate, Kerberos, and OAuth, allowing for secure API testing.
  6. Proxy Support: CURL can be configured to use proxies, making it useful for testing APIs behind different network configurations.
  7. Verbose and Debugging Options: The tool offers detailed output and debugging options that help in diagnosing issues with API requests and responses.
  8. Cookie Handling: CURL can handle cookies, allowing for session-based interactions with APIs.
  9. SSL and Certificate Handling: It provides extensive support for SSL/TLS and certificate handling, enabling secure communication with HTTPS endpoints.
  10. Scripting and Automation: CURL commands can be easily scripted, making it a powerful tool for automation in development and CI/CD pipelines.


CURL has numerous advantages that contribute to its popularity as an API automation tool:

  1. Simplicity and Ease of Use: CURL’s command-line interface is straightforward, making it easy to learn and use for both beginners and experienced developers.
  2. Versatility: Its support for a wide range of protocols and features makes it suitable for many different use cases, from API testing to web scraping.
  3. Cross-Platform: CURL is available on virtually all operating systems, including Windows, macOS, Linux, and Unix, ensuring broad compatibility.
  4. Open Source and Free: CURL is free to use and open-source, which allows for extensive customization and integration into various workflows without licensing costs.
  5. Extensive Documentation: CURL has comprehensive documentation and a large community of users and contributors, providing a wealth of resources for learning and troubleshooting.
  6. Integration Capabilities: CURL can be easily integrated into scripts and automated workflows, making it a powerful tool for continuous integration and deployment processes.
  7. Robustness and Reliability: CURL is known for its stability and reliability, making it a trusted tool for critical tasks involving data transfer and API interactions.


Despite its many strengths, CURL has some limitations:

  1. Command-Line Complexity: While powerful, CURL’s command-line options can be overwhelming for new users, and complex commands can become difficult to manage and remember.
  2. Lack of GUI: CURL is a command-line tool, and the lack of a graphical user interface can be a drawback for users who prefer visual tools for API testing.
  3. Basic Reporting: CURL does not provide advanced reporting features out of the box, which can limit its usefulness for detailed test result analysis and presentation.
  4. Scripting Overhead: For more complex testing scenarios, extensive scripting may be required, which can be time-consuming and less intuitive than using specialized API testing tools.
  5. Limited Built-In Testing Features: CURL is not a dedicated testing tool, so it lacks some advanced testing features such as automated test suites, data-driven testing, and detailed validation mechanisms found in other API testing tools.

Using CURL for API automation is straightforward. Here are some common examples of how CURL can be used to interact with APIs.

Basic GET Request:

curl -X GET ""

POST Request with JSON Data:

curl -X POST "" \
     -H "Content-Type: application/json" \
     -d '{"title": "foo", "body": "bar", "userId": 1}'

GET Request with Custom Headers:

curl -X GET "" \
     -H "Authorization: Bearer YOUR_ACCESS_TOKEN"

File Upload:

curl -X POST "" \
     -F "file=@/path/to/your/file.jpg"

Detailed Output and Debugging:

curl -v -X GET ""

Using Proxy:

curl -x http://proxyserver:port -X GET ""



CURL is an open-source tool and is free to use under the curl license, which is derived from the MIT license. Users can freely download, use, modify, and distribute CURL in their projects without any licensing fees.

CURL is recommended for:

  1. Developers: Developers who need a quick and reliable way to test APIs during development will find CURL invaluable for its speed and ease of use.
  2. QA Engineers: QA teams can use CURL to automate API tests, validate endpoints, and integrate these tests into CI/CD pipelines.
  3. System Administrators: CURL’s versatility makes it useful for system administrators who need to automate interactions with web services, perform health checks, and manage network configurations.
  4. Data Engineers: Data engineers can use CURL for data transfer tasks, such as fetching data from APIs, uploading files, and integrating with various data sources.
  5. Security Professionals: CURL’s ability to handle custom headers, authentication, and SSL/TLS configurations makes it a useful tool for security testing and validation of secure endpoints.
  6. Open Source Enthusiasts: Users who prefer open-source tools and need a reliable, community-supported solution for API automation will appreciate CURL’s capabilities.


CURL is a powerful and versatile tool for API automation and data transfer. Its support for a wide range of protocols, HTTP methods, and features makes it suitable for a variety of use cases, from simple API testing to complex automation tasks. While it lacks some advanced testing features and a graphical interface, its simplicity, robustness, and extensive documentation make it a favorite among developers, QA engineers, and system administrators.

As an open-source tool, CURL provides a cost-effective and reliable solution for API interactions, making it an essential tool in the modern software development and testing landscape. Whether you are looking to perform basic API tests, automate data transfers, or integrate API testing into your CI/CD pipelines, CURL offers the functionality and flexibility needed to achieve your goals efficiently.

About the author
Irfan Ahmad

Irfan Ahmad

Software Quality Leader | Helping software teams to deliver with speed, security and scale.

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