What is an API?
An API, or Application Programming Interface, lets two or more software systems or parts talk to each other. APIs make certain data and functions available while hiding the depth inside.
They are usually divided into three groups: REST, SOAP, and GraphQL. Each group uses a different set of communication methods. REST APIs use HTTP requests to GET, PUT, POST, or DELETE data. SOAP, on the other hand, uses XML messaging methods for more standard interactions.
What are API testing tools?
API testing tools are specialized platforms that help testers and developers build tests to ensure APIs work the way they should. These tools can test many things about an API, such as its security, usefulness, and dependability.
Advanced API testing tools have features like coding, testing in multiple environments, and integrating with CI/CD pipelines.
A free or open-source tool for API testing usually has basic features like simulating requests, running tests automatically, and reporting in real time. This convenience makes them perfect for small teams or organizations that want to save money.
There are several categories of API testing:
Functional Testing: Checks if the API behaves as expected by comparing its output with predefined results.
Load Testing: Examines how the API performs under heavy usage by simulating high traffic conditions.
Security Testing: Verifies the API’s defense mechanisms against common threats like SQL injection and cross-site scripting (XSS).
Integration Testing: Ensures that the API works seamlessly when connected with other systems or services.
List of Top 10 API Testing Tools
1. Postman :
Postman is a platform for developing APIs. It has three parts: Collections, Workspaces, and Built-in Tools. With Postman collections, you can run requests, test and debug, automate tests, create mocks, record, and monitor APIs.
You can also share groups, set permissions, and control who can see what in different workspaces.
Key Features of Postman
While it involves some coding for creating test scripts, the process enables robust automation of API testing tasks.
It facilitates exploratory testing by allowing quick requests and inspection of responses.
It offers compatibility with popular API specifications such as Swagger and RAML, making it easier to import and work with structured API definitions.
The system encourages team collaboration through shared workspaces and documentation capabilities.
The platform provides a comprehensive set of tools—including execution, testing, documentation, and monitoring—within a single platform.
Limitations of Postman
The system is primarily designed for functional testing, with limited support for advanced testing scenarios.
It is best suited for basic operations like verifying response codes, headers, payloads, and schema validations.
The system does not support performance or load testing out of the box.
The system lacks in-depth analytics and real-time performance metrics.
Reusing or adapting Postman test scripts across different projects or environments can be challenging due to limited modularity.
Website: https://www.postman.com/
2. HyperTest
HyperTest is a platform for no-code API testing designed for modern agile teams. It automatically generates integration tests by analyzing real network traffic, eliminating the need for manual test case creation.
Trusted by leading tech teams at Nykaa, Porter, Yellow.ai, Urban Company, Zoop.one, and Skaud, HyperTest ensures that any breaking changes are promptly reported to QA teams. By simulating real user flows through API calls, it identifies issues that traditional testing methods might overlook, often within minutes.
HyperTest’s comprehensive approach includes functional, contract, performance, and security testing, all within a single platform.
Key Features:
It eliminates manual test writing by auto-generating integration tests using real network traffic.
It simulates end-user journeys by testing API calls across real user flows.
It provides a no-code, user-friendly platform that is ideal for both developers and QA teams.
The system detects critical issues and regressions within minutes, thereby speeding up the testing cycle.
Limitations:
It is dependent on existing traffic patterns—it may miss untested or rare edge cases.
It is not designed for performance or load testing scenarios.
There is limited flexibility for custom or highly complex test logic.
Initial configuration may require changes in how traffic is routed or captured.
Website: https://www.hypertest.co/
3. Katalon Platform
Tests for APIs, the web, desktops, and phones can all be automated with Katalon Studio. All frameworks, ALM interfaces, and plugins are included in a single package, which makes deployment easy.
One thing that makes Katalon Studio stand out among the best API tools is that it can combine UI and API/Web services for various environments, such as Windows, Mac OS X, and Linux.
Key Features:
It supports a wide range of protocols, including REST and SOAP, and allows configuration with SSL client certificates.
AssertJ provides fluent assertion capabilities, enabling testers to write tests in a BDD-like style.
Lets users import tests directly from tools and specs like Swagger (both 2.0 and 3.0), Postman collections, WSDL, and WADL files.
It simplifies the process of setting up API test data through its integrated UI testing interface, thereby streamlining test scenarios.
It is suitable for both structured automated testing and flexible exploratory testing approaches.
Limitations:
The free version has limited capabilities, as Katalon operates on a freemium model with advanced features locked behind a paywall.
Compared to other tools, Katalon has a smaller community, which means fewer shared resources or quick solutions.
Handling complex or edge-case scenarios might require extra effort due to limited community-driven documentation.
Does not support a broad range of scripting languages, which may restrict teams preferring flexibility in writing test scripts.
Website: https://katalon.com/
4. Google Apigee
Apigee is a cross-cloud API testing service that is led by JavaScript and has a lot of different features. Its features can be easily accessed by developers and users using different editors. Apigee is great at managing APIs with a lot of data because it is designed to meet the needs of large and complex digital businesses.
Because it can look at API traffic, reaction times, and possible error rates, it is very good at quickly finding and fixing problems that slow things down.
Key Features:
Allows teams to design, manage, and expand APIs effectively from a centralized platform.
Uses a step-by-step, JavaScript-driven workflow for implementing API logic.
Helps identify performance bottlenecks by analyzing API traffic, error rates, and latency.
Makes it easy to generate and deploy cloud-based API proxies using OpenAPI specifications.
Limitations:
Setting up Apigee on-premises can be costly and resource-intensive, especially for smaller organizations.
The deployment process can be complex, though adopting a containerized setup could simplify things.
Might be overwhelming for teams with simpler API needs due to its enterprise-level capabilities.
Advanced features often require the paid version, limiting accessibility for budget-constrained teams.
Website:https://cloud.google.com/apigee
5. Apache JMeter
JMeter is free software that can be used to test an application’s load and speed. As a tool for coders that can work on multiple platforms and at the protocol level, it is very flexible.
It’s worth mentioning that JMeter can be used as a unit-testing tool for testing JDBC database connections. It’s easy to make test data with its plugin-based design, and it has a Command-line mode that works well with operating systems that support Java.
Key Features:
Supports caching and offline storage of test results for easier access and review.
Seamlessly integrates with CSV files, enabling quick generation of dynamic parameter values for API tests.
Allows smooth integration of API tests into CI pipelines through tools like JMeter and Jenkins.
Ideal for performance testing of both static and dynamic resources, ensuring reliability across various scenarios.
Limitations:
The user interface of JMeter is often criticized for being cumbersome, which can make navigating and executing test scripts challenging.
JMeter can be memory-intensive, leading to performance lags compared to other API testing tools.
The process of writing test scripts for API testing in JMeter can be more complex than in other, more intuitive tools available.
Website: https://jmeter.apache.org/
6. Rest Assured
REST Assured is an open-source, free Java tool that is used to test and validate RESTful APIs. Java users like it because it is easy to use, which makes it a popular choice for writers and testers who work with REST services.
Key Features:
Supports all major HTTP methods (GET, POST, PUT, DELETE), allowing seamless interaction with a wide range of API endpoints.
Predefined configurations for requests, such as base URI, headers, query parameters, and authentication, that can be reused across multiple tests for efficiency.
Provides robust capabilities to inspect API responses, including status codes, headers, response bodies, and performance metrics like response time.
Includes built-in support for handling common response formats like JSON and XML, which are widely used in modern APIs.
Limitations:
Not suitable for testing SOAP (Simple Object Access Protocol) APIs, focusing primarily on REST APIs.
Requires a solid understanding of Java programming to use effectively, which might pose a learning curve for beginners or non-developers.
Website: https://rest-assured.io/
7. Karate DSL
Karate DSL, an open-source API testing framework, automates API tests by incorporating Gherkin syntax and Behavior Driven Development (BDD).
This method is different from other behavior-driven development (BDD) tools like JBehave or Cucumber because it offers pre-defined step definitions that make it easy to create tests, even for people who don’t know much about coding.
Key Features:
Follows Behavior-Driven Development (BDD) syntax, making test scenarios more readable and easy to understand.
Designed for beginners, it allows users to write tests with minimal coding experience.
Seamlessly integrates with the Gatling framework for conducting performance and load testing.
Supports parallel test execution using multiple threads, which helps speed up the testing process.
Limitations:
Users may need to familiarize themselves with its custom scripting style, which could take some getting used to.
Lack of IntelliSense (auto-completion) support in many IDEs may slow down script writing and increase chances of syntax errors.
Troubleshooting or pinpointing issues in the code can be a bit challenging without detailed debugging tools.
Website: https://www.karatelabs.io/
8. SoapUI
Many companies like SoapUI, a well-known API testing tool, because it can stick to specific protocols and functionality needs. There are many things it can do, and it works with both REST and SOAP APIs.
SoapUI is an expert in API performance testing, security testing, and mocking, which makes sure that API actions are safe and run smoothly.
Key Features:
Tests how stable your APIs remain under heavy user traffic, helping identify performance bottlenecks.
Offers detailed performance metrics and reports that assist in making informed decisions.
Allows you to simulate test scenarios and analyze results to better understand system behavior.
Comes with built-in security checks for vulnerabilities like SQL injection and cross-site scripting (XSS), ensuring robust API protection.
Can mimic different API behaviors to support end-to-end and isolated testing environments.
Limitations:
Some users have experienced instability, with the tool occasionally crashing during complex or high-volume test runs.
The interface and advanced features can be overwhelming for beginners who are new to API testing.
Relies heavily on well-structured WSDL files for web service testing, which may be a roadblock if those files are missing or poorly defined.
Website: https://www.soapui.org/
9. Blazemeter
BlazeMeter is a powerful API testing tool with many features that make the testing process faster and better. It’s made to meet a range of testing needs, such as functional testing, API monitoring, and speed testing.
Key Features:
Offers an all-in-one platform for conducting various types of tests, including performance, functional, and API testing.
Utilizes AI-powered data generation to enhance the accuracy and coverage of test scenarios.
Smoothly integrates with popular development environments, making it convenient for testers and developers.
Provides access to a top-tier device lab, enabling thorough testing across multiple devices and conditions.
Includes advanced tools for API testing and real-time performance monitoring.
Limitations:
The pricing structure might be a bit steep for small teams or individual users working with limited budgets.
Understanding and interpreting BlazeMeter’s detailed test reports can be challenging for new users, requiring some experience with performance testing tools.
Website: https://www.blazemeter.com/
10. Rest Console
This Chrome-based REST/HTTP Client tool makes it easy to create and test custom HTTP requests that work with any RESTful API service.
Key Features:
Allows users to easily build request bodies for POST and PUT methods using raw data input.
Offers a simple and intuitive interface for editing and managing custom headers.
Streamlines the process of adding and managing query parameters in API calls.
Supports multiple authentication types, including Plain, Basic Auth, and OAuth, providing flexibility for different use cases.
Limitations:
The user interface feels outdated and may not be very accessible or modern for today’s standards.
The tool is still evolving and lacks some advanced features found in more mature API testing platforms.
Website: https://github.com/ahmadnassri/restconsole
When should you choose Open-Source API Testing Tools?
Selecting an Open-Source API Testing Tool: Key Considerations
When choosing an open-source API testing tool, it’s important to evaluate several aspects such as the scale of the project, the skill level of your team, and financial limitations.
Here are situations where opting for a free or open-source solution makes the most sense:
Need for Customization: Open-source tools are highly adaptable. With access to the source code, developers can tailor the tool to suit unique testing requirements, especially helpful when default functionalities fall short.
Budget Limitations: For startups or small teams operating with tight budgets, open-source tools provide a cost-effective way to carry out comprehensive API testing without the burden of licensing fees.
Integration with CI/CD Pipelines: If your team relies on continuous integration and deployment, open-source tools typically support seamless integration with popular CI/CD platforms like Jenkins, CircleCI, and Travis CI—making automated testing part of your regular development flow.
Community Support and Growth: Most open-source API testing tools thrive on active community involvement. This often leads to rapid feature enhancements, collaborative problem-solving, and access to a rich pool of shared scripts and resources.
Conclusion
API testing plays a big role in making sure your applications run smoothly and securely. Whether it’s about checking how features work, testing data flow, or making sure different systems talk to each other properly—it’s all part of building great software. If you’re new to the topic, start by understanding the basics with this guide on What is API Testing and get a clear picture of how REST APIs work.
And if you’re serious about growing your skills, don’t miss out on Edureka’s API Testing Certification. It’s designed to help you gain hands-on experience and stand out in the job market with the right knowledge and practical skills.
API Testing Tools FAQs
What are API testing tools?
API testing tools are software used to test if APIs work correctly by sending requests and checking responses. Popular tools include Postman, SoapUI, Rest Assured, JMeter, Swagger, and Katalon Studio.
What are the 3 types of testing in API?
The three main types of API testing are functional testing, which checks if the API performs its intended operations correctly; performance testing, which evaluates how the API handles load and stress; and security testing, which ensures the API is safe from threats like unauthorized access and data breaches.
What is the best API tool?
Postman is considered one of the best API testing tools due to its user-friendly interface, powerful features, and wide adoption by developers and testers.
Is Postman an API tool?
Yes, Postman is an API testing tool used for developing, testing, and managing APIs.