10 API Testing Tools You Should Know

What Are API Testing Tools? 

API testing tools are software that enables developers and testers to check API functionality, performance, security, and reliability. They are designed to send calls to the API and receive responses, checking for correct behavior. API testing is critical because it can identify potential bugs, inefficiencies, and vulnerabilities in APIs early in the development lifecycle, which can prevent significant problems down the line.

Many organizations today rely heavily on APIs for communication between systems and services. Therefore, ensuring their reliability and performance is crucial. API testing tools help by providing a mechanism to validate the API's responses against expected outcomes, ensuring that they work as intended.

This is part of a series of articles about API Testing

What to Look for in an API Testing Tool? 

Here are a few important features an API testing tool should provide:

Seamless Integration with CI/CD Pipelines

Continuous Integration and Continuous Delivery (CI/CD) is a software development practice that enables frequent code changes, faster bug fixes, and rapid product delivery. API testing tools should be able to seamlessly integrate with your CI/CD pipelines.

With CI/CD integration, the development team can automate the testing process, ensuring that the APIs are validated at every step of the development process. This saves time and resources while reducing the risk of manual errors. It also facilitates early detection and resolution of issues, enhancing overall software quality.

Ability to Perform Concurrent Random Tests

An API testing tool should have the ability to send multiple requests to the API simultaneously and in random order, mimicking real-world scenarios. This is particularly important when testing APIs that are expected to handle high traffic loads. 

By performing concurrent random tests, you can stress-test your API and identify any performance issues before they become a problem in a live environment. This also helps in uncovering potential race conditions, deadlocks, and other concurrency-related issues.

Fast Response Time

Developers need a fast feedback loop when developing and modifying APIs. An API testing tool should be able to execute tests quickly, providing immediate feedback on the API's performance. This encourages developers to test APIs on an ongoing basis and allows developers to identify and rectify issues as part of their day-to-day development process.

Tzvika Shneider

CEO, Pynt

Tzvika Shneider is a 20-year software security industry leader with a robust background in product and software management.

Tips from the expert

• Prioritize open-source tools with a large community: Choose open-source API testing tools like Postman and Insomnia for flexibility, while leveraging community support for best practices.
• Combine functional and security testing: Select tools that offer both functional and security testing capabilities, streamlining the API testing process.
• Automate contract testing: Use tools like Pact to automate contract testing between services, ensuring all APIs conform to agreed-upon specifications.
• Incorporate testing tools into CI/CD: Integrate chosen API testing tools into your CI/CD pipeline to ensure continuous validation of API behavior in every deployment.
• Leverage tools with API mocking: Opt for API testing tools that include mocking capabilities to simulate endpoints and test various scenarios efficiently.

10 Notable API Testing Tools

1. Pynt

Pynt emerges as a comprehensive solution in the realm of API security, meticulously crafted to address the multifaceted challenges faced by organizations in protecting their digital interfaces. At its core, the platform is engineered to conduct extensive security assessments of APIs, unveiling vulnerabilities that could potentially be exploited by cyber adversaries.

The primary objective of Pynt.io is to fortify the security of APIs, which are integral to the operational fabric of modern digital applications. As these interfaces facilitate critical data exchange and system interactions, their security is paramount. Pynt.io employs advanced testing methodologies to scrutinize APIs, ensuring they are not only resilient against known security threats but are also fortified to withstand emerging vulnerabilities.

Beyond mere detection, Pynt stands out by offering in-depth analysis and actionable insights. It empowers developers and security professionals with detailed reports and recommendations, enabling them to understand the intricacies of the identified vulnerabilities and to implement robust security measures effectively. Moreover, Pynt.io prioritizes compliance with global security standards, ensuring that APIs adhere to stringent regulatory requirements.

The Pynt API security testing suite is designed for effortless integration into existing development ecosystems. Operating directly within the Postman app, Pynt acts as a wrapper for Newman (Postman's command-line companion), ensuring a smooth and intuitive testing experience. It's readily integrated into RestAssured and PyTest scripts with a single command line, streamlining testing processes. Additionally, Pynt seamlessly melds into popular CI/CD pipelines, including GitHub Actions, GitLab, and Jenkins, enhancing deployment workflows with robust security testing that's both efficient and effective

Related content: Read our guide to api testing types

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2. Postman

Postman is a popular API testing tool known for its user-friendly interface and robust set of features for API development and testing. It enables developers and testers to send requests to APIs, view responses, and automate testing sequences. Postman can handle various HTTP methods and authentication mechanisms. 

Postman offers scripting capabilities that can support complex tests and workflows, making it ideal for both simple and advanced API testing needs. Additionally, it offers extensive collaboration features, enabling teams to share and manage their API testing environments effectively.

Related content: Read our guide to api security

3. Pytest

Pytest stands as a powerful, yet user-friendly, testing framework favored for its expressive and straightforward approach to API testing. It simplifies test code creation with its assert-based syntax, while offering extensive plugin support for customization. Pytest's integration with libraries like Requests ensures robust testing of API responses, making it an ideal choice for clear, concise, and scalable API testing solutions.

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4. REST-assured

REST-assured is a Java library specifically tailored for testing RESTful web services in the Java ecosystem. It simplifies the process of sending HTTP requests and receiving responses. REST-assured's syntax is highly readable and easy to use for writing and maintaining test scripts.

The tool integrates seamlessly with existing Java testing tools, such as JUnit and TestNG, allowing for automated API testing within these frameworks. REST-assured has a given/when/then syntax, which is inspired by behavior-driven development (BDD) practices. This makes it useful for API testing while aligning with modern development methodologies.

Related content: Read our guide to api test automation

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5. Insomnia

Insomnia is a versatile tool for API design, debugging, and testing, known for its user-friendly interface and powerful features. It simplifies the process of creating, organizing, and executing HTTP requests, making it an essential tool for developers working with REST, GraphQL, or gRPC APIs. Insomnia's ability to manage multiple environments, set up reusable variables, and visualize responses ensures a smooth and efficient workflow, making API testing and debugging a more intuitive and productive experience.

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6. Apigee

Apigee, now part of Google Cloud, is a platform that provides API management capabilities along with testing features. It is designed to help organizations in developing and managing APIs efficiently. While its primary focus is not on API testing, Apigee offers tools for API monitoring and diagnosis, which are essential in ensuring API performance and health. 

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These capabilities enable developers to identify and address issues in real-time. Apigee also provides security features to protect APIs from malicious attacks, allowing it to manage the lifecycle of APIs, from creation and testing to deployment and monitoring.

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7. SoapUI

SoapUI is specifically designed for testing SOAP (Simple Object Access Protocol) and REST (Representational State Transfer) APIs. It offers a platform for creating, executing, and analyzing API tests. 

SoapUI can handle functional testing, performance testing, and security testing. The tool supports automated testing, and its interface makes it easy to create complex tests with multiple steps and assertions. SoapUI also integrates well with other development tools.

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8. Katalon

Katalon Studio is an automated testing platform that supports both API and UI testing. It is designed to be accessible to all testers, from beginners to experts. Katalon provides a comprehensive set of features for API testing, including support for various types of requests, assertions, and parameterization. 

The tool's ability to integrate API and UI tests into the same environment is particularly beneficial for end-to-end testing scenarios. Katalon also integrates with popular CI/CD tools, enhancing its utility in DevOps practices.

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9. Cypress

Cypress is a front-end testing tool that, while primarily focused on testing browser-based applications, can also be employed for API testing. It offers functionalities for testing RESTful APIs. Cypress allows for sending various HTTP requests to APIs and asserting the responses, making it a useful tool for verifying the behavior of APIs in the context of a web application. 

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Cypress offers fast and consistent testing capabilities suitable for modern web applications, where front-end components interact extensively with APIs. Cypress's real-time reloads and debugging capabilities enhance the developer experience, making it easier to write, test, and debug code

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10. JMeter

Apache JMeter stands out in the realm of open-source software for its robust performance testing capabilities, particularly for web applications and APIs. It offers an intuitive interface that simplifies the creation and execution of detailed test plans. 

Key features that make JMeter a go-to tool for API testing include its ability to simulate multiple users and concurrent threads, accurately mimicking real-world traffic and stress conditions on APIs. Whether it's RESTful or SOAP APIs, JMeter ensures comprehensive testing, providing insights into how APIs perform under varied loads and user scenarios, all while maintaining ease of use and efficiency.