Top 6 Tools to Test Rest APIs


Rest APIs are a vital part of every digital application nowadays. It’s crucial to verify that APIs are working fine before applications are delivered to end-users. Rest APIs testing is carried out manually as well as automatically. When testing Rest APIs, we send various HTTP/S requests using GET, POST, PUT, PATCH, and DELETE methods to ensure that the functionality is working great. Rest APIs testing also includes validating response versus the defined inputs, checking the accuracy of response, and checking HTTP status codes and error codes.

There are many open source and commercial testing tools that can be used to test Rest APIs. Within this article, let’s analyze the best fit among them for your testing demands.


Testerum is one of the latest tools in the automation testing field. This tool is free & open-source, and very convenient to use due to its user-friendly UI. It uses behavior-driven development (BDD) to illustrate test scenarios and does not require any programming skills.

When it comes to testing APIs, the best advantage of Testerum is that you can create complex API flows using it. How Testerum defines HTTP Requests is similar to Postman, but it provides an easy and innovative way that doesn’t require programming knowledge to verify the HTTP Responses.

The Testerum UI will increase the efficiency and effectiveness of the learning process, allowing newcomers to get started with the tool easily. Ultimately, it will help to reduce the cost of training employees.

Moreover, Testerum can be integrated with any CI/CD environment. Docker images are available and can be used to run Testerum tests easily in any CI/CD environment. It helps developers to maintain continuous integrations and development without distracting the existing development process. Since Testerum is extensible with all JVM languages, it allows developers and testers to create their own integrations.

Testerum has a centralized reports server and provides quality reports and statistics about test data and test results. While being an interesting tool, Testurum is still very young in the field and has only a small community around it. There’s also a lack of documentation and online helping community due to its novelty.

Katalon Studio

Katalon Studio is another test automation tool that supports testing Rest APIs. It is a free tool built on Appium and Selenium. However, it’s not open-source and can be run on multiple OSs like Windows, macOS, and Linux. This tool has a moderate learning curve and requires basic programming skills for using it. It can be integrated into CI/CD environments using Docker. Furthermore, it generates reports and statistics about test data. In contrast to Testerum, Katalon has a big community to help with difficulties.

Some of the most significant advantages of the Katalon Studio are having hundreds of built-in keywords for creating test cases and supporting one of the most powerful assertion libraries, AssertJ, to build fluent assertion with BDD style.

Katalon also has few downsides, such as the need to have programming skills for testers and buy a training pack to implement the tool in a large team even though it’s a free tool. Finally, it’s not an extensible tool like Testerum.


Rest-Assured is an open-source testing tool built on top of Java. With this tool, users don’t have to write codes from scratch since it has a bunch of baked-in functionalities. It can also be integrated with Maven and CI/CD. On top of that, Rest-Assured supports BDD Given/When/Then syntax so that users don’t need to have much expertise in HTTP to use the tool. That syntax makes code more readable and cleaner.

Rest-Assured can also be integrated with the serenity automation framework enabling testers to combine both UI and REST tests into one framework and generate reports.

The most important thing about Rest-Assured is that it has methods to fetch data from every single part of the request and response no matter how complex the JSON structures are. Therefore, this tool is very simple and straightforward.

However, two main drawbacks of this tool are the need for sound Java programming knowledge to use it and not having an inbuilt report generation facility.


Postman is a scalable API testing tool that can be used for both automated and exploratory testing. This tool supports Windows, macOS, and Linux and has the ability to mock APIs. Furthermore, Postman can be integrated with the CI/CD environment, and developers use it as an API development environment. This tool does not require coding knowledge so that it can be used smoothly by both developers and testers for API testing.

The run, test, document, and monitoring feature of Postman allows testers to share the knowledge with the team easily. It is done by enabling them to package up all the requests and expected responses and then sharing them with team members. Postman offers extended support for GraphQL requests and schemas. Besides, testers can submit the request as a JSON, text, JavaScript HTML, and XML request as well as form data.

Apart from the above advantages, Postman also has some downsides. It doesn’t offer a good solution for monitoring test cases. Verifying HTTP responses is very difficult with Postman as it requires advanced programming knowledge.

Karate DSL

Karate DSL is a Gherkin-based API testing tool built on top of Cucumber. It is a BDD testing framework and includes multiple steps with Given/When/Then/And/But syntax. Therefore, users can start testing very quickly without writing step definitions, and even non-programmers can write test scenarios using this tool. Karate DSL comes with the report generation facility and facilitates configuration switching/staging and multithreaded parallel execution.

Since Karate DSL is a young API testing tool, it has a small community. There are also limited documentation and tutorials for it, and the documentation can be improved further.


SoapUI is a leading API testing tool designed by SmartBear. It supports data-driven testing and comes as a free as well as a pro version. The Pro version supports native CI/CD integrations and asynchronous testing. It has a very user-friendly GUI and convenient for functional testing as users can test complex scenarios without writing any background scripts. SoapUI also facilitates options for test debugging that lets users monitor the execution step by step.

However, SoapUI requires programming knowledge to verify API responses and script automation. Therefore, it is very complicated for beginners. Not enabling complex flows for testing is another downside of SoapUI.


This article has discovered the top testing tools which help to achieve the best Rest APIs testing performance. Not every testing tool fits your application. Using this, you should be able to select the most suitable testing tool for your demand.