14 Open Source API Testing Tools For REST & SOAP Services


14 Open Source API Testing Tools For REST & SOAP Services

As we move towards more Agile shift-left software development processes like continuous integration and delivery, the need to quickly give test feedback to our developers is increasing.

One downfall to UI tests is they are slow, making them a poor choice for letting developers know quickly if their code has broken the latest build or not. API tests, on the other hand, tend to be faster and run more reliably than GUI tests.

Before we take a closer look at the api testing tools, let’s make sure we’re all on the same page with what an API actually is.

 What is an API?

Application Programming Interfaces (API) is a specification that acts as an interface for software components.

While most functional testing involves testing a user interface like a web page or a dot net form, API testing involves bypassing a user interface and communicating directly with an application by making calls to its APIs.

API testing allows you to test headless technologies like JMS HTTP, databases and Web services.

API testing is sometimes called “headless” testing. Most headless testing consists of bypassing the UI and sending a request directly to an application’s backend or service and receiving a response, while validating the response to ensure things are working as we expect them to.

This simple example is often referred to as a client/server relationship. A client makes a request by asking for a resource; the request then goes out and finds a server that can fill that request. The server locates the desired resource and sends a response back to the client.

What API Testing Tools Can I Use to Automate API Testing?

Since Selenium is just for browser based testing, you may be wondering which tool to use for Rest and Soap web service-based testing.

Here are some of the top API testing tools that can be used for Rest and Soap Web Service Testing.

Postman Mail

Postman is a rest client that started off as a Chrome browser plugin but recently came out with native versions for both Mac and Windows.

At a high level, you can use it to send a post request to your web server and it gives you the response back. It allows you to set up all the headers and cookies your API expects, and then check the response when it comes back.

  • Can be used for both automated and exploratory testing
  • Can be run on Mac, Windows, Linux &Chrome Apps
  • Has a bunch of integrations like support for Swagger & RAML formats
  • Has Run, Test, Document and Monitoring Features
  • Doesn’t require learning a new language

Karate DSL karate

Karate allows you to create a test that can sequence calls to any kind of web-service and assert that the responses are as expected.

  • Build on top of Cucumber-JVM
  • Can run test and generate reports like any standard Java project
  • Test can be written without any Java knowledge required
  • Tests are easy to write even for non-programmers

Check out a quick example on how to get started using Karate with BDD.

SoapUI soap

SoapUI is a headless functional testing tool from SmartBear software. It comes in two flavors: Free open source version and Pro Version. Since the free version is open-source, you can actually gain access to the full source code and modify as needed. The pro version is user-friendlier, and has additional functionality including a form editor, an assertion wizard for Xpath, and SQL query builder.  The free version lets you:

  • Can easily create custom code using Groovy
  • Drag and Drop Test Creating
  • Can create complex scenarios
  • Asynchronous Testing
  • SoapUI’s Mock Service lets you mimic web services before they are implemented

HttpMaster Express HTTP

HttpMaster describes itself as a web development and test tool to automate testing of web sites and services. It can be used to test RESTful web services and API applications. HttpMaster also allows you to and monitor API responses.

  • HttpsMaster project offers global options to customize your API request
  • Parameter capabilities enable you to include dynamic data with your request
  • You can use request chaining to leverage request items to include some data from previous request with the next request

Rest- Assured rest

Rest-Assured is an open-source Java Domain-specific language (DSL) that makes testing REST service simple. It simplifies things by eliminating the need to use boiler-plate code to test and validate complex responses. It also supports XML and JSON Request/Responses.

  • Removes need to create boilerplate code required to interact with a rest service
  • Support BDD Given/When/Then syntax
  • Integrated seamlessly with Java projects

RestSharp Sharp

RestSharp is a simple REST and HTTP API Client for .NET

  • Supports .NET 3.5+, Silverlight 5, Windows Phone 8, Mono, MonoTouch, Mono for Android
  • Easy installation using NuGet for most .NET flavors

Rest Console Console

HTTP Client and Request Visualizer and Constructor tool, helps developers build, debug and test RESTful APIs. Rest Console is a HTTP Request Visualizer and Constructor tool, helps developers build, debug and test RESTful APIs.

  • Easy query parameters creation
  • Syntax highlighting
  • Authentication support: Plain, Basic, OAuth + Custom

RoboHydra Server 

RoboHydra is a testing tool for HTTP-based clients (ie. software that makes HTTP requests). The idea is, instead of connecting your clients-under-test to the real server, you connect them to RoboHydra and make RoboHydra respond with whatever you need for each request.

  • You can test many different kinds of clients
  • Written in Javascript, runs under Node 

Hippie-Swagger Peace

hippie-swagger is a tool for testing RESTful APIs. It’s also an API testing tool with automatic swagger assertions. In addition to validating API behavior, it will fail tests when swagger documentation is missing or inaccurate.

  • Can validate All aspects of swagger file validated; parameters, request/response body, paths, etc.
  • Accurate, human readable assertion messages

WebInject inject

WebInject is an open source solution for automated testing of web applications and web services. It can be used to test individual system components that have HTTP interfaces (JSP, ASP, CGI, PHP, AJAX, Servlets, HTML Forms, XML/SOAP Web Services, REST, etc).

  • Is a command line tool
  • Written in Perl can be installed on MS Windows, GNU/Linux, BSD, Solaris, MAC OS


PyRestTest is a python based REST testing and API microbenchmarking tool

  • You can write your tests in basic YAML or JSON config files, no code needed
  • Returns exit codes on failure
  • Only works on Mac and Linux

Airborne Plane

Airborne is an open source Ruby based RSpec driven API testing framework.

  • Works with Rack application like Sinatra and Grape
  • Works with APIs written in Rails


Recommended by Unmesh Gundecha Unirest is a lightweight HTTP request client libraries.

  • Can be combined with xUnit, BDD runner to make it a test tool

Mockbin Bin

Mockbin was recommended by Augusto Marietti. Mockbin allows you to generate custom endpoints to test, mock, and track HTTP requests & responses between libraries, sockets and APIs.

  • Mock Custom Endpoints
  • Create Custom HTTP Methods
  • Log and inspect incoming calls to your custom endpoints

Api Testing Tools Recap

These are the top API testing tools I’ve come across, but there are tons of API testing tools popping up everywhere, so I’ll definitely be adding to this list as time goes on.

If one of your favorite API test tools is not listed, please let me know and I’ll add it.

Baskaran - May 18, 2017

Regularly following yours blog and reading the articles, it helps to me more passionate about the automation tools and motivates to try and use the tools.
Thank you :)

Tony du'Gay - May 18, 2017

I’m a big fan of Soap UI. In my latest project I have used it successfully for load testing – what I liked about that was I was reusing my functional tests for load testing. I also used the Pro version for pen testing – again, getting some reuse from my functional tests. It is possible to add security tests with the open source version but I find it a lot more cumbersome.

Patrik S - May 18, 2017

Great insights related to the API testing tools by Mr. Joe. These will definitely help to deal with API testing. In addition to the mentioned tools, I would like to add the tool named Testing-Whiz. This is a code-less test automation tool for web, API, database, mobile apps, etc. This tool helps you to test whether your application communicates and accesses functions correctly from the Web by effectively verifying the behavior of web services connected to them.

    Joe Colantonio - May 18, 2017

    Thanks Patrik – is testing-wiz open source? I left out paid options in favor of open sourced solutions for this list

Christian - May 18, 2017

I’m a fan of post man to test out my understanding of contracts and creating collections. My favorite API automation tool is Gatling. It’s marketed as a load testing tool, but it lends itself well to integration/end-to-end testing too. I’ve completely tested business flows from login to cart checkout at the API layer via automation with Gatling.

Antoine - May 18, 2017

Hi Joe,
Nice list! It appears I’ve got new things to try out :)

Do you now Restlet Client? It’s a visual tool that lets you create and execute test scenarios. See https://restlet.com/modules/client/

It’s not open source, but offers a lot of features for free (same model as Postman).

Ronald Alversado - May 18, 2017

JMETER should be on the list. We currently use it for Automated API test.

Peter Thomas - May 19, 2017

Great list ! But Joe, is HTTP really master open-source ? It does seem to have a free edition – but appears to be closed-source + commercial.

Rasool Saheb - May 19, 2017

Very good info about all open source tools..Thanks Joe

Nikolay Advolodkin - May 23, 2017

Great collection of resources Joe. Thanks for that! Postman is great and simple to use.

elwin wildschut - May 29, 2017

I feel you miss powershell on the list
+ 1 line just to import your wsdl
+ 1 line to just send in your request and get your output
+ Installed on all (windows) machines so reusable quickly by all people in your company
+ Easy to learn (google: Powershell API testing)
+ very fast (as you just do all stuff from commandline no UI overhead)
– The scripting language from powershell maybe less easy to learn with cmdlets

Burak - June 15, 2017


Mikael Fransson - June 24, 2017

Missing Insomnia, https://insomnia.rest/

Cross platform, open source. Beautiful UI.

Vishvanath Kumar - June 29, 2017

Thanks for this information……

I need one more help from admin and viewers

little bit I have confusion “Which tool should I use for API testing”


Suresh - September 5, 2017

Thanks for the tutorial!

I have one question:

Web Services testing is (part of / one type of) API Testing – Am I right?

Why API Testing is called differently (from Web Services Testing).

For me, API Testing is equal to Web Services testing (i did this with Soap UI).


Burdette Lamar - September 7, 2017

I have put example Ruby code for testing a REST API in my GitHub project:


Ashwin Gangadharan - October 24, 2017

Hey, we use https://www.runscope.com/ for API testing, because of some limitations we are planning to replace it.

For UI we use Selenium with JAVA. I am searching for API testing tool which provide software-as-a-service.

Please suggest me a good suitable tool for API testing which also has Report generation.

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