What are API and API testing tools?

Ever wondered how Google Maps was able to locate your current location and show you the nearest exit when you were stranded in the middle of god-knows-where? 

Well, that’s Google Maps API doing the work.

An API (Application Programming Interface) is, in simple terms, the messenger that enables two software to share data and talk to each other. But how do an application remain fully functional, as it’s designed to every time, without compromising on user privacy? The answer is API testing tools.

Read More: Top 10 Best Examples For APIs

Benefits of API testing in Agile

Using API testing tools is how development and testing teams qualify software performance before they get to the users’ hands. Now guided by the principles of Agile, the main benefits QAs and developers are: 

• Earlier testing and feedback without waiting for the whole software to be completely built
• Faster test maintenance and refactoring
• More bugs and issues were spotted in less time compared to UI tests

Read more: API Testing Benefits

To better understand API Testing, read through our comprehensive lists of API Testing interview questions.

How To Choose Good API testing Tools?

The number of API testing tools on the market for you and your team to try out and select will probably take forever. That’s why we have listed a few key considerations for you to keep in mind.

• Basic API Requirements: Does it support the majority of the HTTP requests? Can settings and artifacts be imported from one project/test to another to save time?
• Complexity: Make sure the skillsets in your team are able to learn and use the software in the shortest time possible.
• CI/CD Integration: Check its list of integrations to see if the tool works with CI systems your team is using, like Jenkins or Bitbucket, and also if it’s native to avoid extra time trying to configure everything.   
• Interoperability: Can the tool be connected to communication platforms like Slack, project management systems like Jira, and Git for version control or your team’s toolchain?
• Non-technical Friendly: Read the tools’ documentation to see if they support BDD conventions and are able to export easy-to-understand reports.   

Top 15 API testing tools on the market

According to the State of Quality Report 2024, currently Katalon Studio, Postman, and JMeter the top API testing tools in their respective area of focus, with Katalon Studio loved by 37% for its versatility in testing any AUT, Postman favored by 45% of users as great for API tests, and JMeter by 31% for supporting performance testing. You can have a look at the table below for a brief comparison of them, along with REST-assured and Apigee, which are great options also.

1. Katalon Studio 

Recognized as the Gartner Peer Insights Customers’ Choices for Software Test Automation for three consecutive years, Katalon is the leading test automation solution for API, Web, and Mobile and Windows applications. To make your API testing effortless, Katalon offers up to 3 testing modes:

1. No-code: Utilizing the Record-and-Playback functionality, you have the ability to capture their manual on-screen actions and transform them into automated test scripts that can be executed repeatedly. Absoultely no code is needed!
2. Low-code: Katalon also offers a library of Built-in Keywords, which are essentially pre-written code snippets featuring customizable parameters tailored for specific actions. For instance, a keyword like "Click" streamlines the internal logic to locate an element (e.g., a button) and execute the click action, requiring the tester only to specify the target element without delving into the underlying code.
3. Full-code: You can seamlessly switch to Scripting mode and independently compose the test script, and switch back to no-code and low-code modes whenever you want. These two modes complement the full-code option, providing the advantages of both worlds: the ease of test creation through point-and-click mechanisms and the flexibility of in-depth scripting. This approach shifts the focus from the intricacies of writing tests to what needs to be tested, significantly enhancing productivity.

Interested? Check Out The Capabilities of Katalon 
 

Feature highlights:

• Easy-to-use UI and productivity-centric features for projects of all sizes
• Supports REST, SOAP requests, and SSL client certificates
• Enable test import from Swagger (2.0 & 3.0), Postman, WSDL, and WADL
• Native CI/CD integrations (Jenkins, Azure DevOps, CircleCI, Dockers, etc.)
• Data-driven testing methods better test coverage and reliability
• AssertJ support to create fluent assertions in BDD style
• Support API test data setup using UI testing 
• Built-in reporting platform to centralize reports and activities across tool stacks: version control systems, CI/CD, test automation tools, and ALMs
• Free API testing courses and tool tutorials on Katalon Academy

Pricing: Free and flexible paid plans

Download Katalon and Witness its Power in Action
 

2. Postman

Originally a Chrome browser plugin, Postman extended to an on-premise solution for both Mac and Windows.

Feature highlights:

• Easy-to-use REST client
• Offer rich interface 
• Available for both automated and exploratory testing
• Able to run on Mac, Linux, Windows
• Provide many integrations like support for Swagger & RAML formats
• Run, test, document, and monitoring features

Users could share the knowledge with the team at ease as they can package up all the requests and expected responses, then send them to their coworkers.

In the latest 10.6.0 version, Postman uses new advanced preferences to help users smartly organize the collections and API elements (mock servers, monitors, tests, and documentation) generated from API schemas. You can use data files to test your APIs with different data points. You can also configure the scheduled run to send email notifications if there are any test failures or errors.

Website: https://www.getpostman.com/

Pricing: Free – $12/user/month

Read More: Top 15 Postman Alternatives For API Testing

3. Apigee

Apigee is a cross-cloud API testing tool enabling users to measure and test API performance, support and build API. Apigee also provides PCI, HIPAA, SOC2, and PII for apps. This tool has been named one of the leaders in the 2019 Gartner Magic Quadrant for Full Lifecycle API Management four times in a row.

Feature highlights:

• Allows design to monitor, implement and extend API 
• It is multi-step and powered by Javascript 
• Define performance issues by tracking API traffic, error rate, and response time 
• Easily create an API proxy based on open API specifications and deploy it in the cloud 

This tool is designed for digital businesses and the data-rich mobile-driven APIs and apps that power it. Since version 4.19.01 in 2019, Apigee gives users more flexibility to manage their APIs with features (e.g., Open API 3.0 support, TLS security, Self-healing with apigee-monit, and Virtual host management improvements). Now, the latest version is enhanced with minor bug fixes and security improvements. Overall, it is feature-rich and well-recognized by users.

Website: Cloud Apigee

Pricing: Contact Sales

4. JMeter

Initially, JMeter was created for performance testing, however, it is commonly used for functional API testing.  

Feature highlights:

• Cache and offline replay of test results
• Automatically work with CSV files, thus enabling the team to create unique parameter values for the API tests at speed
• Able to include the API tests in CI pipeline thanks to JMeter and Jenkins integrations 
• Available for both static and dynamic resources performance testing

The latest release JMeter 5.5 is packed with versatile features and enhancements such as new themes, bug fixes, visual representation of disabled elements, revamped Groovy library, and updated JMeter templates for functional testing. This tool is most suitable for Web application performance and load testing.

Website: JMeter Apache

Pricing: Free

Read More: Top Performance Testing Tools For Your Team

5. REST-assured

This open-source Java Domain-specific language enables testing REST services more simply. It can be used to validate and verify the response of these requests.

Feature highlights:

• Offer a bunch of baked-in functionalities to help users proceed with the codeless practice
• Integrates seamlessly with Serenity automation framework, thus users can combine the UI and REST tests in one framework that extracts excellent reports
• Support BDD Given/When/Then syntax
• Supports POST, GET, PUT, DELETE, OPTIONS, PATCH and HEAD requests
• Users do not need to be an HTTP expert to utilize this tool

Version 5.3.0 supports Spring Framework 6, and fixed many issues with the initial OSGi support. The latest version 5.3.0 is released with various improvements and bug fixes.

Website: Rest-Assured

Pricing: Free

6. Assertible

Assertible is an API testing tool that focuses on automation and reliability.

Feature highlights:

• Support automating API tests throughout CI/CD pipeline
• Assist in running API tests after deployments and integrates with familiar tools (e.g., GitHub, Slack, and Zapier)
• Support validating HTTP responses with turn-key assertions
• Help testers update their tests when their specifications change by The Sync feature. Hence it’s needless to manually update tests after adding new parameters or changing the response of the API

In October 2019, Assertible added the Encrypted variables feature, which provides a new way to store passwords, tokens, and secret data fields. This offering is to improve API testing security practices. 

Website: Assertible

Pricing: Free – $25/month 

7. Soap UI

This headless functional testing tool is dedicated to API testing. It allows users to test REST and SOAP APIs and Web Services with no hassles.

For the Free package, users can:

• Acquire the full source code and build their preferred features at hand
• Create tests effortlessly with Drag and drop, Point-and-click
• Reuse load tests and security scans for functional test cases in just several steps with Reusability of Scripts feature

For the Pro package, users can:

• Powerful data-driven testing – which means users can simulate how consumers interact with the APIs thanks to data loaded from files, databases, and Excel 
• Support native CI/CD integrations and asynchronous testing

The latest version SoapUI 5.7.0 includes support for GraphQL APIs and offers other improvements that make API testing more convenient and powerful. SoapUI now disables the Load and Save project scripts by default to enhance testing security.

Website: SoapUI

Pricing: Free – $749/year

8. Karate DSL

This new API testing tool assists users in creating scenarios for API-based BDD tests simply without writing definition steps. Indeed, KarateDSL creates those definitions itself, thus users can quickly kickstart the API testing. 

Feature highlights:

• Build on top of Cucumber-JVM
• Run a test and generate reports likewise to any standard Java project
• Supports configuration switching/staging, multithreaded parallel execution 

The latest revision, Karate UI 1.3.0, allows for Java 8 and introduces a slew of new features, including redesigned HTML reports, call-Single-Cache, Karate Robot Windows for Windows Desktop app automation, and enhanced tree walking in UI Tests. Also, Karate UI allows you to write tests in any language that can handle HTTP, JSON, or XML.

Website: Karate

Pricing: Free

9. Rest Console

This tool is a REST/HTTP Client for Google Chrome that enables users to visualize and construct custom HTTP requests to test with any RESTful API service.

Feature highlights:

• Construct POST or PUT body via raw input
• Support to modify custom headers through intuitive UI
• Assist users in creating query parameters with ease
• Able to be used for several authentications like Plain, Basic, OAuth 
• Supports customizable interface

The most recent release, Rest Console v4.0.2, has been upgraded with several features to enhance user experience and bug fixes (e.g., oAuth improvements, Collapsible sections, Clickable Links in Response, UI enhancements).  

Website: RestConsole GitHub

Pricing: Free

10. API Fortress

Testers and developers can create and automate functional tests si

nce API Fortress is a continuous platform for API testing.

Feature highlights:

• Easy-to-use intuitive UI for any skill level
• Plug-and-play stimulates your continuous API Testing  
• Support Web Services, Test REST, SOAP, GraphQL, and Microservices
• It’s a web-based collaborative tool for teams that helps testers work within a browser and requires no downloads.

The latest version in September 2020 offers many new features which allow a test to continue after a fatal error, improve multipart for on-prem and load testing, and K/V store for mocking services. API Fortress is free to use and easy to customize to the specific requirements of your project.

Update: API Fortress Cloud (legacy) solution was discontinued on October 15, 2022

Website: API Fortress

Pricing: Contact sales

Read more: API Testing Tips for Beginners and The 50+ API Interview Question

11. Pyresttest

It is a Python-based REST API testing platform that supports tests in JSON or YAML config files, no coding knowledge is required.

Feature highlights:

• Generate and validate mechanisms to build complete test scenarios
• Allow easy deployment on-server for smoke tests/health checks with minimal dependencies (pycurl, pyyaml, optionally future)
• Returns exit codes on failure to slot into automated configuration orchestration tools 

In 2016, the latest 1.7.1 version was released with a fixed JSONschema extension in Python 3 and added test coverage. This tool is best used for RESTful APIs.

Website: Pyresttest

Pricing: Free

12. Hoppscotch

Hoppscotch is a tool in the API tool category of the technology stack. It is a free and fast API request generator with a minimalistic UI design, allowing you to send requests and get/copy responses in real-time. Therefore, you can create requests faster, saving valuable development time. In August 2021, Hoppscotch was updated to version v3.0.1, with some minor bugs being fixed. As an open-source tool, you can feel free to customize it to your project requirements.

Website: Hoppscotch

Pricing: Free

13. Taurus

Taurus is a free and open-source framework for simple and direct API testing because it is easy to learn. Taurus helps you hide the complexity of running performance tests without learning any programming languages; instead, all you need to understand is the basic YAML structure of Taurus.

Taurus v1.16.19 updates various features, improves user experience, and fixes bugs.

Website: Taurus

Pricing: Free

14. Citrus Framework

The tests provide a Java fluent API to specify the test logic and are fully automated. Citrus can act on both sides as a client or a consumer during the test when replacing the actual request/response message over the wire.

Citrus 3.3.0 is the latest stable version. It is available in the central Maven repository so that you can add Citrus as a Maven dependency to your project. It’s a free, open-source tool with custom scripting functionalities that you can utilize your programming skills to fit project requirements.

Website: Citrus Framework

Pricing: Open-source

15. Airborne

Airborne is an API automation testing framework with a Ruby-based RSpec-driven framework. Since Airborne is a programming framework, it has no user interface apart from the text file to create code. Besides that, to use Airborne testers need to remember a few critical methods in the toolset and some Ruby and RSpec fundamentals.

In 2020, Airborne was updated to version v0.3.7 with minor bug fixes. It is a free-to-use and open-source API testing tool that testing teams may use to meet their requirements.

Website: Airborne

Pricing: Free

Although we have introduced some of the best testing tools on the market, it is essential to keep the pros and cons in mind. You may need to be flexible in trying various options before finding the one that best suits your requirements.