8 Top Open-Source API Testing Tools In 2021


API Testing refers to Artificial Programming Interface Testing which is a type of software testing. That emphasizes on if the developed APIs meet the projection performance, functionality, reliability, and security. API means the bunch of software procedures and different functionalities through the software are operated or executed. Also, API integration solutions have become the base of the modern development of the software as the applications are more interested in adopting the microservices approach in the software development process.

Due to the current scenario of pandemics, most of the day-to-day processes are being handled from home only and through exclusive apps. Thus, the e-commerce business has grown. The small business people are also keen to be available on apps to reach out their existing customers and create a new customer base. Thus, the demand of API Integration for eCommerce has also seen a drastic upwards shift from the past.


Below mentioned are some of the best tools of API testing which have made the overall testing process much easier.

1) Ready API

-It works on different platforms like Linux, Mac, Windows and can be easily integrated in any environment.
-It provides API performance testing, API functional testing, API security testing
-It acts as a base platform for load testing of different web services like Graph Ql, SOAP, RESTful.
-For Automated testing, it supports Command-Line, also it helps in job queuing and parallel execution of the functional tests.
-It reduces and completely omitting the dependencies during the testing and development process.
It has also become an essential part as it helps to integrate the different functionalities of the shipping process.
-Provides native support for Jenkin, Azure, Docker etc.
-It works best for DevOps and Agile teams.

-It is a free debugging tool which was developed by Telerik
-It is one of the best choice tools which is used by developers and testers who work on HTTPS for building APIs.
-The main job of Fiddler is to check for the network traffic between a computer and the internet.
-It ensures that the proper headers, cash directives, and cookies are transferred well between the client and the server.
-Here the responses are created with mock requests, responses, auto-responders which allows the testing of websites without manipulating the code.
-It supports all the frameworks like Java, .NET, Ruby etc.

3) Katalon Studio
-This can be used by any programmers for testing who have or do not have testing or programming experience.
-It helps to create very fluent assertions in BDD style with support of Assert J.
-It provides very insightful dashboards of test reports for all the stages of testing.
-It braces CI/CD integration and also supports SOAP and Rest
-It is very helpful in exploratory and automated testing.
-It has many pre-built and customizable code templates, also sample projects are provided for quick reference.

– Other than free services, it also provides paid solutions for small business enterprises and small teams.

4) SoapUI
-It is one of the most widely used tools for API testing.
-Here, one can reuse the functional test cases, thus the reusability of the scripts saves a lot of money.
-It seamlessly integrates with a large number of API management platforms and completely supports SOAP, REST, JMS etc.
-It is thoroughly data driven testing. One can load the data from excel sheet which consists of the details of how the consumers interact with the APIs.
-It is used by major companies all around the world like to name a few: Pfizer, NASA, Cisco, Microsoft, Apple etc.

5) Postman
-It is in the form of a plugin of the Google browser which can be easily used for testing. It also provides solutions for both Mac and Windows.
-It has distinguishing features like run, test, documentation, and monitoring.
-Here the developers or programmers do not need to learn any new language.
-Both types of testing are facilitated by it like automated and exploratory.
-POSTMAN is the most reliable API tool for exchange of REST information.
-Boolean Test can be written with the interface of POSTMAN.
-One unique thing about POSTMAN is that it has a rich interface which makes it really easy to use.
-It supports RAML (RESTful API Modeling Language) formats as well as SWAGGER.

6) Tricents
– It is a continuous testing tool for Agile and DevOps and supports different arrays of protocols like RabbitMQ, SOAP, REST, IBM MQ, TIBCO EMS etc.
– Model based test automation maximizes reuse and maintainability.
– The duration of regression testing is reduced automatically.
– It helps with sustainable automation with the invention of new technology.
– API tests can be used across different devices like mobile, desktop etc., cross browser, thus, enables end-to-end testing.

  • Some known customers of this tool are Exxon Mobil, Toyota, Allianz, Starbucks, BMW, Deutsche Bank, Vodafone, UBS and many more.

7) Apigee

-It is a cloud-based API testing tool which allows you to measure and test API performance. And it also supports other tools like Swagger.
-It supports Node.js and provides a customizable developer portal.
– It provides are Java & Python callouts, distributed traffic management, IP whitelisting.
-Apigee is such a tool built for certain purposes of digital business along with the data rich mobile drive APIs and applications.
-It creates API proxies from open Specification and then deploy them on cloud.
-It also keeps track of the performance issues like error rates, response time, tracking API traffic etc.

8) Karate DSL

-It is an open-source API testing tool developed by Intuit a few years back, also this framework is based on cucumber library.
-A tester can test the web services by writing down the tests in any domain-specific languages.
-Any developer or tester can easily write the tests, even the one with basic knowledge of HTTP, XML, XPATH, JSON will be good enough to work on Karate DSL.
– Generating the required reports like a standard Java project and allows the switching of configuration.
-It supports multithreaded parallel communication.
-It allows re-use of the payload data and user-defined functions across all the tests.


The above writeup explains about some of the best API testing tools available in the industry. But not one tool fits all the sizes, thus, everything depends upon the requirement and utility. Not one tool can be called an ideal tool as some of the tools have features of the commercial players like Postman. Some of them are open-source solutions and are easily available for everyone like Karate DSL. Some of the tools are such that they are available at affordable cost and provide some decent features also like Postman, Katalon Studio. Thus, the developer or tester has to select as per their requirement.

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