API testing (Application Programming Interface Testing) is a software testing type which focuses on the determination if the developed APIs meet expectations regarding the functionality, reliability, performance, and security of the application.
The interest in API/Web services testing has been growing steadily over the last couple of years, according to Google Trends. Research by Smartbear over 5,000 software professionals in 2017 showed that the number of API testers automating more than 50% of their tests is expected to grow by 30% (from 59% to 77%) in the next two years. In addition, 80% of survey participants reported that they were responsible for some API testing.
Having the right process, tool and solution for API automation test are more critical than ever. API testing is a crucial component of a success CI/DevOps practice.
This article will provide a summary of the top API testing tools covering both open-source and commercial solutions that testing teams can select to suit their needs. SoapUI, Katalon Studio, and Postman are the top-three tools in the list.
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 a just several steps
- Quickly create custom code using Groovy
- 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
Pricing: Free - $659/year
2. Katalon Studio
Katalon Studio is a free test automation tool for API, Web and Mobile applications. It is emerging as a leading tool for API/Web services testing and positioning itself as a comprehensive end-to-end automation solution for both developers and testers.
Katalon Studio supports both SOAP and REST requests with various types of commands and parameterization functionalities. Moreover, the capability of combining UI and API/Web services for multiple environments (Windows, Mac OS, and Linux) has been considered a unique advantage of Katalon Studio among the top API tools.
- Support both SOAP and Rest
- All-in-one shop for API, WebUI and Mobile testing and the combined capabilities among those.
- Support data-driven approach.
- Can be used for automated and exploratory testing
- Support CI/CD integration.
- Support AssertJ, one of the most potent assertion library, to create fluent assertion with BDD style
- Suitable for both non-techies and pros via Manual and Groovy Scripting modes.
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.
Pricing: Free - $21/user/month
4. 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
Tricentis has recently introduced Interactive Testing, allowing test managers to invite external manual testers — who do not use Tosca — to execute test cases and collect results without having to configure Tosca environments. In other words, this new feature provides the ability to execute manual testing without installing Tricentis Tosca.
Pricing: Contact Sales
Apigee is a cross-cloud API testing tool, allowing users to measure and test API performance, supports and build API using other editors like Swagger.
- Allows the design monitor, deploy, and scale APIs
- Identify performance issues by tracking API traffic, error rates, and response times
- Easily create API proxies from the Open API Specification and deploy them in the cloud
- Cloud, on-premise, or hybrid deployment model on a single code base
- PCI, HIPAA, SOC2, and PII for apps and APIs
- Apigee is purpose-built for digital business, and the data-rich mobile-driven APIs and apps that power it.
With the latest version of Apigee, you can create an alert for a target and use their Investigate dashboard to view information about target services defined by the Service Callout policy.
Pricing: Free trial - $2,500/month
JMeter (open source) is widely used for functional API testing although it is actually created for load testing.
- Supports replaying of test results
- Automatically work with CSV files, allowing the team to quickly create unique parameter values for the API tests.
- Users can include the API tests in CI pipelines thank to the integration between JMeter and Jenkins
- It can be used for both static as well as dynamic resources performance testing
Since the most recent release in September 2018, JMeter 5.1 has been packed with new core enhancements, improved user experience, and many bug fixes, such as creating a test plan from a cURL command, live reporting and web report, HTTP samplers and test script recorder.
Pricing: Open source
Rest-Assured is an open-source Java Domain-specific language that makes testing REST service more simple.
- Have 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
Starting from version 4.0.0, REST Assured requires at least Java 8, instead of Java 6 as was previously required. This version also added support for Apache Johnzon and fixed a lot of issues with the initial OSGi support.
Pricing: Open Source
Assertible is an API testing tool which concentrates on the automation and reliability.
- Support for automating API tests through each step of a continuous integration and delivery pipeline.
- Support for running API tests after deployments and integrates with familiar tools like GitHub, Slack, and Zapier.
- Support validating HTTP responses with turn-key assertions such as JSON Schema validation and JSON Path data integrity checks
Assertible recently added a new feature called Sync. This feature allows testers to update their Assertible tests when their specifications change. This also means that users no longer have to manually update your tests after adding new parameters or changing the response of your API.
Pricing: Free - $500/month
9. Karate DSL
Karate DSL is a new API testing tool which help 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, multi-threaded parallel execution
Starting from version 0.9.3, Karate UI is no longer part of the open-source tool’s core but a separate Maven artifact. Also included in this version is built-in support for WebSocket that is based on the async capability.
Pricing: Open Source
10. No one-size-fit-all tools
It hurts, but true!
We believe the list above nominates the best solution available out there if you are planning to adopt API automation testing. However, like most of the solutions in this industry, finding the ideal-one-tool to do it all is almost impossible.
Some may find the features of the commercial players (Postman, Tricentis Tosca,…) are sufficient but the costs of ownership will be the show-stop factor. Open source solutions (Rest-Assured, Karate DSL,…) are affordable but require skilled resources and effort to implement the right frameworks. Tools which seem to be a relative balance between cost and other factors (Katalon Studio, Postman) might have drawbacks to specific project types that need to be considered.
API testing established its trend in automation testing, and more tools will be developed to serve the growing demands of the software development teams. Finding the perfect tool is still tough, but we have the good news that you have way more choices than before. Carefully considering your requirements, pros and cons of each solution — try not too ambitious at the early stage and trialing the top 5 relevant candidates from the list above. With the POC for these solutions created, you will have a better knowledge of your project’s critical factors and fine-tune your shortlist. This approach gives you a good chance to identify the suitable tool for the current status and information of the next choice when your project is more mature.
This article was last modified in June 2019. I will continue to regularly update the latest top API testing tools and their functionalities. Leave a comment below if you have any suggestions on API testing products!