API Testing: Which tool is the best?

API testing (Application Programming Interface Testing) is a software testing type which focuses on the determination of the developed APIs meet expectations regarding the functionality, reliability, performance, and security of the application.
In such a scenario, people mentioned API testing as a must-have step in many workflows. This blog can help you understand why the demand for API testing increasing and which tools could be suited for your project in 2020.

What is API?

API (Application Programming Interface) is a computing interface that enables communication and data exchange between two software systems. It also contains the terms of this data exchange.

There are 3 types of API:

  • Private APIs:

Available for Internal applications only.  The private strategy allows a company to fully control the API usage.

  • Partner APIs

These APIs are shared with business partners who have signed an agreement with the publisher. Partner APIs are used most for software integration between two parties.

  • Public APIs

These APIs are available for any third-party developers to access and integrate into their software. Public API’s providers vary from big technology firms such as Google, Amazon, or Facebook to individual developers.

Why are APIs more and more popular?

With Agile development becoming the standard in the most product teams, how we develop software and automate tests have changed adequately. 

Moreover, Integration testing focuses on verifying that the interactions of many small components can integrate together correctly. So, service testing leans to be quicker and more reliable than GUI tests.


Source: https://www.simplilearn.com/agile-vs-devops-article

Furthermore, coupled with the rising popularity of Agile and DevOps, it results in shift-left, with the QA process becoming earlier than the waterfall model. When testing starts earlier, teams are focused on the quality and get the mindset “coding right the first time.” These reasons lead to the replacement of API testing.

As API testing is demanding in software development,  testers and QA teams must choose a qualified API testing tool to best utilize its benefits.

Top list for API testing tool:



Postman is built for API development, testing, and managing APIs for QA professionals. Postman was first developed as a side project for simplifying API workflow and testing projects. 

Highlight feature:

  • Ease of use: A new user to Postman needs to sign up, download, and log in to their account to get started.
  • Simplified API: Postman users can begin their API journey quickly
  • Robust testing capabilities: 
  • Integration and collaboration powered.

Postman is ideal for manual testing needs — a fast and simple way to test APIs.  However, the world is turning their focus more toward continuous testing tools. This is Postman’s limitation: It is hard to ensure stability in performance and lacks a reporting mechanism. 

Besides, below are some other ideal automation testing tools for your reference: 

Katalon Studio

katalon studio

Katalon is a complete, easy-to-use, and scalable automation platform for continuous testing. The tool supports several types of the application under test, including API, mobile, web, and desktop application testing. With extended features, the application makes API testing much faster and more convenient for reporting and team collaboration. In case you are already familiar with Postman and need a way to sync all your API data into Katalon Studio, check out this Postman migration guide.

Highlight feature:

  • Handles API, Web, desktop and mobile tests across platforms
  • Allows testers and developers to collaborate and share test cases easily
  • Hundreds of built-in keywords for creating test cases
  • Supports AssertJ to create fluent assertions using the BDD style
  • Seamless integration with other ALM tools for CI/DevOps practices

Website: https://www.katalon.com/

Further reading: API testing guide with Katalon for beginners from here.


soap ui

It is an open-source and headless functional testing tool specifically designed for API testing. SoapUI is supported by Smartbear, and has been downloaded more than 3 million times. With this tool, you can do Functional Testing, Performance Testing, Interoperability Testing, Regression Testing, and much more.

Highlight feature:

  • Robust data-driven testing with data from files and databases
  • Generates tests easily 
  • Mocks services with RESTful mocking
  • Asynchronous testing

Website: https://www.soapui.org/



Assertible is an API testing tool that concentrates on automation and reliability. This tool provides simple and powerful assertions to test and monitor your APIs and websites. Although Assertible just had been founded in 2015, it has grown gradually and attained achievements for its effort in the testing tools market. 

Highlight feature:

  • Support for automating API tests through each step of a continuous integration and delivery pipeline.
  • Support for running API tests after deployments and integrates with familiar tools like GitHub, Slack, and Zapier.
  • Support validating HTTP responses with turn-key assertions such as JSON Schema validation and JSON Path data integrity checks.

Website: https://assertible.com/


API testing will endure essentially in the software testing market. Tools like Postman, Katalon, SOAP UI, and Assertible have great potential for further development with more values for its users. However, it is also crucial for firms to pick the right tool that is able to scale up with their projects. 

Check out here for more article with Selenium Easy

Katalon Studio: 

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