API or Application programming interface is a set of functions and procedures that allow the creation of applications that access the features or data of an operating system, application, or other services. For API testing you generally send calls to the API, you get the output and log what the system responded.

There are many open-source tools for API testing available in the market. We will look at few of the best tools among them.


    Tricentis is one of the best web services testing tools. Some of the outstanding features of Tricentis are:-

  • It does integrate in DevOps and Agile cycle

  • It supports a broad range of protocols including HTTP(s) JMS, Rabbit MQ, NET TCP, TIBCO EMS, AMQP, SOAP, REST, IBM MQ.

  • It makes script maintenance easy as it uses model-based test automation.

  • It makes it possible to do end-to-end testing as you can use API tests across mobile, packaged apps, cross-browser, etc.

Few of the world’s big brand names like HBO, Toyota, BMW, Starbucks, Vodafone, Telstra, Allianz, Whole Foods, Orange, Deutsche Bank are among the customers of Tricentis.


Postman started as a Google Chrome browser plugin, however, it recently rolled out with native versions for both Windows and Mac. It is a robust HTTP client to test web services. With the use of Postman, you can set up all the cookies and headers that your API expects, and check the response when comes out.

  • It can extract almost all modern Web API data

  • It can be used for automated and exploratory testing

  • It is compatible with Chrome apps, Mac, Windows, and Linux,/p>

  • Not being a command based tool. It makes easy to paste text into command line window.

  • It is more reliable when it comes to transmitting and receiving REST information.

  • It does not make it compulsory to learn a new language.


It is one of the most effective tools for automated REST API testing. It also offers automated recording of REST/ RESTful/ HTTP APIs.

Apart from it’s Easy-to-use Interface and great Customer Support Team, there are some other features that make vREST standout from other tools.

  • Record and Replay : You can simply record test cases by manually using your application once.

  • It provides vrunner to quickly validate your API

  • No skilled resources are required to validate your web application.

  • With the help of Mock Server Functionality, you can create API mocks.

Testing API


SOAP UI is the world’s most trusted API testing tool. It offers the industry’s most comprehensive and easy to learn functional testing capabilities. You can test REST and SOAP APIs with ease. Pro version of SOAP UI is user-friendly and it also has functionalities like a form editor, SQL query builder and an assertion wizard for XPath, With Free version, you can

  • Easily create custom code using Groovy

  • Create complex scenarios

  • Drag and drop test creating

  • Mock service can allow you to mimic web services before they are implemented.


Karate helps you to script a sequence of calls to any kind of web services and make sure that responses are expected. Payload validation engine can execute a ‘smart compare’ of two JSON and XML documents without being affected by white space or the order in which data-elements actually appear, and you can ignore the field that you choose.

  • Can run a test and generate reports like and standard Java projects

  • No Java knowledge required to write tests

  • Easy to write tests for even non-programmers


It is harder to test and validate REST services in Java in compare to dynamic languages such as Ruby and Groovy. Rest assured is the tool that brings the simplicity of using these languages into the Java domain. It makes things simple by removing the need to use boiler-plate code to test and validate complex responses.

  • It Supports BDD Given/When/Then syntax

  • It integrates seamlessly with Java projects


It is a tool to test RESTful APIs. Hippie-swagger uses hippie, which is an excellent API testing tool.

  • It has all features that the Hippie has.

  • It ensures that Swagger file accurately describes API behavior

  • It shows accurate human readable assertion messages

API Fortress

API Fortress is specially built to work across different teams in major enterprises. It is an automated testing and monitoring platform. It is a browser-based platform and works for REST or SOAP, in the cloud or on-premises.

  • It generates comprehensive test with a single click

  • It does not require any code

  • It generates 100s of tests in a minute

  • It can do full lifecycle functional testing, performance monitoring, and load testing

  • It can generate tests from RAML, Postman Collections, OAI/Swagger

  • It has functionality of editing tests in simple GUI or IDE code view


HttpMaster is popular web development tool with functionalities like web application testing, including API testing, service testing and website testing. It is mainly used as web API test tool to automate testing of web API calls.

  • It creates batches of connected requests to entirely automate REST API or website workflow

  • It imports Swagger data to conveniently create HttpMaster project for your REST API

  • It has functionality of pause/resume which execute request items in desired order along with progress monitoring

  • Compatible with XML, HTML, JSON, CSS and some other web data formats


Parasoft makes it’s place in top ten testing tools as it is feature-rich SOAP testing tool which supports end-to-end testing and has a very user friendly interface. It takes less effort to generate test case as any test case generated with help of Parasoft are reusable and easily maintainable.

  • It supports various platforms like Java, C, C++, or .NET

  • It does not require scripting or coding to design tests

  • It simplifies testing of GUI-less APIs

This was the list of top 10 API testing open source tools. Having described all functionalities, you can simply choose which one best suits your project and get the best outcome with least effort.

For more information on any Web Development project related needs you can contact us at Amar Infotech as we have more than 5 years of IT field experience with clients from across the world.