Top Free API Testing Tools (Genuine Reviews)

The Software Testing Trends for 2018 indicated that APIs (Application Program Interface) are important to successful digital transformation and there is an increasing demand for API testing at a greater level of automation. It comes as no surprise because many companies nowadays require strong API performance and shifts towards APIs architecture. However, the main utilization of test automation now focuses on UI while most API testing is carried out manually. Therefore, the testers need to equip with intelligent and easy-to-use automation tools to test APIs, helping to reduce time-to-market and improving testing effectiveness and productivity.

If you know how important APIs are, this article is for you. It is a comprehensive list of the best, free API testing tools that help to get your work done more quickly, with greater effectiveness, and zero budget spent! Let’s investigate and find out the best fit for your project and testing demands.

Top 5 Free API Testing Tools

1. Katalon Studio

Katalon Studio is a free automation test tool that provides a common environment to create and execute UI functional, API/Web services, and mobile testing. The capability to combine UI and Business levels (API/Web services) for different environments (Windows, Mac OS, Linux) has been considered an advantage of Katalon Studio.

• Katalon Studio supports SOAP and RESTful requests with various types of commands (GET, POST, PUT, DELETE) with parameterized capability.
• Support combination test between UI and API verification
• Support testing both SOAP and RESTful requests
• Hundreds of built-in keywords for creating test cases
• Support one of the most powerful assertion libraries, AssertJ, to create fluent assertion with BDD style
• Support data-driven approach
• Can be used for both automated and exploratory testing
• Suitable for both pros and non-techies

2. Soap UI

SoapUI is a headless functional testing tool dedicated to API testing, allowing users to test REST and SOAP APIs and Web Services easily.

Using SoapUI, users can get the full source and build the preferred features besides these abilities:

• Create tests quickly and easily with drag and drop and point-and-click
• Quickly create custom code using Groovy
• Powerful data-driven testing: Data loaded from files, databases, and Excel so that they can simulate how consumers interact with the APIs
• Create complex scenarios and support asynchronous testing
• Reusability of Scripts: load tests and security scans can be reused for functional test cases in a just a few steps

For advanced features, you need to subscribe SoapUI Pro version (659$/year), which provides an assertion wizard for Xpath, a form editor, and a SQL query builder.

3. Postman

Being originally a Chrome browser plugin, Postman now extends their solution with the native version for both Mac and Windows.
Postman is a good choice for API testing for those who don’t want to deal with coding in an integrated development environment using the same language as the developers.

• Easy-to-use REST client
• Rich interface that makes it easy to use
• Can be used for both automated and exploratory testing
• Can be run on Mac, Windows, Linux, and Chrome Apps
• Has a bunch of integrations like support for Swagger and RAML formats
• Has Run, Test, Document, and Monitoring Features
• Doesn’t require learning a new language
• Enables users to easily share the knowledge with the team as they can package up all the requests and expected responses, then send to their colleagues.

4. Rest-Assured

Rest-Assured is an open source, Java, and domain-specific language that makes testing REST services more simple.

• Has a bunch of baked-in functionalities, which means users don’t have to code things from scratch.
• Integrates seamlessly with Serenity automation framework so that users can combine the UI and REST tests all in one framework that generates awesome reports.
• Support BDD Given/When/Then syntax
• Users don’t necessarily need to be an HTTP expert

5. Karate DSL

Karate DSL is a new API testing tool, which helps create scenarios for API-based BDD tests in a simple way without writing step definitions. Those definitions have been created by KarateDSL so that users can kickstart the API testing quickly.

• Build on top of Cucumber-JVM
• Can run a test and generate reports like any standard Java project
• A test can be written without any Java knowledge required
• Tests are easy to write even for non-programmers
• Supports configuration switching/staging, multithreaded parallel execution

Explore more API Testing Tools (both open-source and commercial solutions)

Which API Testing Tool?

Not every tool meets the needs of every organization. This article has come across the top free tools, which helps you achieve the best API testing performance. So by now, you could be able to decide which ones best fit your testing demands.

Last but not least, the list is unstoppable. There are thousands API Testing tools available out there. If your favorite ones are not listed, please let us know. I would love to update and add more tools to this list.