There are many free and open source performance testing tools available for your API testing tool-kit. Whether you’re using JMeter, Loadrunner, Grinder, SoapUI or any other stand-alone tool – knowing where to find the best tools for this task will save you a lot of time and keep cost at a minimum.
In this article, I will outline the top free Rest API Performance Testing tools. These tools can be used to test throughput, latency, generate load and attack your apis from different locations. Many of these tools are open source and can be used to check performance of development and production environments.
REST-Assured
When using Java, REST-Assured is my first choice for API automation. In fact, it’s the main tool I use for API testing.
REST-Assured is a fluent Java library you can use to test HTTP-based REST services. It’s designed with testing in mind, and it integrates with any existing Java-based automation framework. The REST-Assured API was created so that you don’t necessarily need to be an HTTP expert.
It provides a behavior-driven development (BDD)-like, domain-specific language that makes creating API testing in Java simple. It also has a bunch of baked-in functionalities, which means you don’t have to code things from scratch.
Bonus: If you’re like me and use the Serenity automation framework, you will like that REST-Assured integrates seamlessly with it, which means you can combine your UI and REST tests all in one framework that generates awesome reports.
Testing and validating REST services is harder in Java than it is in dynamic languages such as Ruby and Groovy. This is one more reason to use REST-Assured, since it brings the simplicity of using those languages into the Java domain.
If your team is made up mainly of Java coders, I highly recommend REST-Assured for API testing.
Postman
Some folks don’t want to code in an integrated development environment using the same language as the developers. After all, if your developers don’t contribute to your automation efforts, why force yourself to use their tech stack when it’s not the best option for you?
Sometimes you just want a quick and dirty API test without all the overhead, or you need a tool to help with exploratory testing of your API. Postman is perfect in these scenarios. But it’s also powerful enough that you can create more integrated solutions if you wish.
Postman is an easy-to-use REST client, and you can get started with it quickly by leveraging its Chrome plug-in. There are native versions for both Mac and Windows.
Postman has a rich interface that many REST clients don’t have, making it easy to use. It also lets you easily share your knowledge with your co-workers, because you can package up all your requests and expected responses and send them off to someone else so that he or she can take a look.
Casual gaming company Big Fish Games uses Postman as a collaborative tool. According to Amber Race, a software development engineer in test (SDET) at the company, one person does the research and figures out all the test cases for the API.
That person then publishes that information to a wiki so that others can run the API tests and ensure that what they’re doing doesn’t break existing API functionality. Postman even allows you to place a button on your internal website saying, “Run in Postman,” and it automatically kicks off your Postman tests.
If your team wants to not only test APIs but also have a tool to help automate some of your exploratory API testing efforts, Postman is a great choice.
Citrus Framework
The Citrus Framework can help you automate integration tests for virtually any messaging protocol or data format.
Among its benefits:
- It works with REST, SOAP, HTTP, JMS, TCP/IP, and other protocols.
- It creates tests using Java or XML.
- It’s mature; version 1 launched in September 2009, and it’s been steadily updated ever since, with release 2.7.6 introduced in June 2019.
- It has great documentation.
If you plan to test other headless technologies beyond REST services, Citrus is the tool for you. It’s made to handle any headless protocol, offering an excellent solution for all your non-UI testing needs. This flexibility is beneficial if you work in an enterprise environment and need to test many different kinds of applications.
PowerShell
You might be saying, “PowerShell? Really?” Yes. Really.
With the adoption of DevOps in Windows-based organizations, PowerShell is awesome at automating lots of things from the command line.
Some benefits of using PowerShell for API testing are:
- You need only one line of code to import your Web Services Description Language.
- You need only one line of code to send in your request and get your output.
- It comes factory-installed on all Windows machines, so it’s available to all of your company’s employees.
- It’s easy to learn.
- It’s very fast, since it runs from the command line without any UI overhead.
PowerShell is an open-source Microsoft product. So pretty much anytime you want to use the command line or automate anything, such as API tests inside the Windows ecosystem (or pretty much any Microsoft product), you should go with PowerShell.
Katalon Studio
Katalon Studio is a free test automation solution for APIs, web applications, desktop apps, and mobile applications. It is quickly becoming a prominent tool for API/Web services testing, promoting itself as a complete end-to-end automation solution for developers and testers.
Katalon Studio supports SOAP and REST requests, as well as a variety of commands and parameterization features. Furthermore, Katalon Studio’s ability to combine UI and API/Web services for different platforms (Windows, Mac OS, and Linux) has been cited as a distinct feature among top API tools.
Feature highlights:
- Support both SOAP and Rest
- All-in-one shop for API, WebUI, Desktop App, Mobile testing, and the combined capabilities.
- Support data-driven approach.
- Support automated and exploratory testing
- Support CI/CD integration.
- Support AssertJ, one of the most potent assertion libraries, to create fluent assertion with BDD style
- Suitable for both non-techies and pros through Manual and Groovy Scripting modes.
- Can be integrated with Katalon TestOps — test orchestration platform.
Katalon Studio has been named one of the 2020 Gartner Peer Insights Customers’ Choices for Software Test Automation, with over 600 favorable evaluations, confirming its position at the forefront of the field.
Website: https://www.katalon.com
Pricing: Free — $69/license/month
SoapUI
SoapUI is a headless functional testing tool dedicated to API testing, allowing users to test REST and SOAP APIs and Web Services easily.
Free package: Using the free package of SOAPUI, users can get the full source code and build their preferred features.
- Create test quickly and easily with Drag and drop, Point-and-click
- Reusability of Scripts: load tests and security scans can be reused for functional test cases in just several steps
Pro package:
- Powerful data-driven testing: Data loaded from files, and databases, and Excel so that they can simulate how consumers interact with the APIs
- Support native CI/CD integrations, asynchronous testing
The latest version SoapUI 5.6, released in July 2020, has updated third-party libraries (org.apache.HTTP components, commons-logging, commons-codec, and JUnit) and removed unused third-party libraries (Jackson, KeenIO). To enhance testing security, SoapUI now disables the Load and Save project scripts by default.
Website: https://www.soapui.org/
Pricing: Free – $709/year
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 which makes it easy to use
- 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
- Enable 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.
Starting from version 7.3 in 2020, Postman helps users better organize the collections and API elements (mock server, monitors, tests, and documentation) generated from API schemas by using the new advanced preferences. The latest version 8.7.0 for Mac, Windows, and Linux App has been released in June 2021 with “Warnings” in API validation, with the addition of Security Warnings enabled for all APIs on Postman.
Website: https://www.getpostman.com/
Pricing: Free – $12/user/month
Tricentis Tosca
Tricentis Tosca is a continuous testing platform for Agile and DevOps. Benefits of Tricentis Tosca include:
- Supports many array of protocols: HTTP(s) JMS, AMQP, Rabbit MQ, TIBCO EMS, SOAP, REST, IBM MQ,NET TCP
- Integrates into the Agile and DevOps Cycle
- Maximize reuse and maintainability with model-based test automation
- API tests can be used across mobile, cross-browser, packaged apps, etc…
- Achieve sustainable automation with new technology
- Reduce the time of regression testing
- Interactive testing provides test managers with the ability to execute manual testing and collect results without having to configure Tosca environments.
With the latest version — Tricentis Tosca 14.2 LTS, you can expand Tosca Data Integrity to access data sources that aren’t natively supported. To conduct row-by-row comparisons or load data into the cache database, you may create a bespoke solution and connect it into Tosca Data Integrity.
Website: https://www.tricentis.com/
Pricing: Contact Sales
Postwoman
Postwoman, an alternative to Postman, is a new tool that has gained in popularity over the past few months. It has a clean and modern UI that makes creating API requests fast and easy.
Features that Postwoman is known for include:
- The ability to run everything online (no install required)
- Support for multiple platforms and multiple devices
- The ability to access it from anywhere
- High customizability
If you need to start testing APIs and don’t want the hassle of having to install bloated software on your machine, this tool is for you. It has received almost 15,000 stars on GitHub, a good indicator that folks are getting value from it.
Conclusion
If you’re thinking of testing your API, you’ve come to the right place. In this article, we take a look at some of the best open source API testing tools and commercial API testing tools available today – and we cover some great examples of what they can do, and how we can use them.