An API or Application programming interface is defined as a collection of software functions and procedures that is used to access or execute other software applications. API testing is a software testing type that ensures if the developed APIs are executing correctly and meeting the expectations regarding its functionality, reliability, performance, and security of the application.

With a digital transformations, the demand for API testing is increasing with a greater level of Automation. Hence, testers/QA Engineers/SDET needs to equip themselves with intelligent and easy-to-use automation tools to test APIs that can help reduce the manual efforts to test these APIs and improve testing effectiveness and productivity.

Below are the top tools that can be used to test APIs:

1. SoapUI: SoapUI is the most widely used popular tool for API testing and it allows users to test REST and SOAP APIs easily.

• Create test cases quickly and very easily with its drag-and-drop, point-and-click functionality. These functionalities makes complicated tasks like working with XML and JSON quite simple.

• It is able to create complex scenarios and supports asynchronous testing.

• It allows to reuse the functional test cases as load tests and security scans in just a few clicks.

• It is able to load data from excels, files, and databases and helps in simulating the it the same way as customers interact with APIs.

• It can be easily integrated with 13 API management platforms and supports REST, SOAP, IOT and JMS.

1. Postman: Postman is a chrome browser plug-in and it can be used for testing the APIs. Postman has extended its solution with the native version for both Windows and Mac.

• Almost all modern API data can be extracted with Postman.

• It can be used for both automated and exploratory testing.

• Boolean tests can be written within Postman Interface.

• Postman is more reliable for transmitting and receiving REST information.

• Collection of REST calls can be created and each call can be saved as a part of collection for execution in future.

• It provides support for Swagger and RAML formats.

• It enables users to share the knowledge very easily by creating up the package of all requests and expected responses.

1. JMeter: JMeter is an open source widely used tool for functional API testing. It also includes the features that help to boost the performance of API testing.

• It automatically works with CSV files and allow the test team to create unique parameter values for API tests.

• Replaying of test results is being supported by JMeter.

• It is used for both static and dynamic resources performance testing.

• JMeter is integrated with Jenkins, hence allow the users to include the API tests in CI/CD pipeline.

1. Katalon Studio: Katalon Studio is a free automation test tool that provides a common environment to create and execute API tests. It supports SOAP and REStful request with various types of commands like GET, PUT, POST, DELETE.

• It supports testing of both SOAP and RESTful requests.

• It supports a combination of tests between UI and API verification.

• It supports AssertJ which is the most powerful assertion library, to create fluent assertions with BDD style.

• It is used for both automated and exploratory testing.

• It contains hundreds of built-in keyword to create test cases.

• It supports data-driven approach.

1. Rest-Assured: Rest-Assured is a popular open source framework to test REST services in Java.

• It contains number of in-built functionalities, that means it is not required to code things from scratch.

• It supports BDD: Given/When/Then syntax.

• It can be integrated seamlessly with Serenity automation framework and helps the user to combine the UI and REST tests all in one framework that generates good reports.

• The users don’t need to be an expert in HTTP.