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API testing tools

16 min read



January 8, 2024

12 Best API Testing Tools To Ensure Reliability But Not Issues In 2024

12 Best API Testing Tools to Ensure Reliability But Not Issues in 2024

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Selecting the right API testing tool is a crucial decision that directly impacts the efficiency and reliability of software development processes. The landscape of API testing tools is diverse, with each tool offering unique strengths tailored to different needs. 

Ultimately, the best API testing tool depends on a development team's specific needs, preferences, and project requirements. Whether prioritizing simplicity, performance, or comprehensive API management, each tool in this diverse landscape has its strengths, and the optimal choice hinges on aligning these strengths with the unique demands of the development environment.

If you need assistance choosing the right tool set, we are here to help you. Reach out to us, and we will choose the best API testing tools for your project.


Apigee is a tool for managing API gateways facilitating data exchange between cloud applications and services. It acts as a proxy, concealing the backend services' APIs. Apigee consists of two main components. Firstly, Apigee services enable API proxy server creation, deployment, and management. Secondly, the Apigee runtime environment processes and handles all API traffic. AI-based monitoring of APIs allows the quick identification of any issues with just a few clicks.

Apigee covers the entire API lifecycle, including API design, development, testing, deployment, and monitoring. This end-to-end approach allows organizations to manage APIs efficiently.

Full API lifecycle management

Apigee provides robust analytics and monitoring capabilities, allowing users to gain insights into API usage, performance, and potential issues.

API analytics and monitoring

Apigee includes security features such as OAuth authentication, API key management, and traffic encryption, ensuring that APIs are secure and compliant with industry standards.

Security features

Apigee is designed to handle large-scale API deployments, making it suitable for enterprises with complex API requirements. It can scale horizontally to accommodate increasing API traffic.


Apigee supports deployment in various cloud environments, providing flexibility for organizations that operate in multi-cloud or hybrid cloud architectures.

Multi-cloud deployment


Apigee's feature richness may be overkill for simple projects or small-scale API implementations. Organizations with less complex requirements may find simpler tools more suitable.

Complexity for simple projects

Apigee is a commercial platform, and its pricing model may not be suitable for small or budget-constrained projects.


Users opting for Apigee as an API testing tool are bound to the Apigee platform. Other standalone tools might be more suitable if an organization prefers a more independent or lightweight testing solution.

Dependency on the Apigee platform

Apigee's testing capabilities are more integrated with its API management features, and it may not be as well-suited for offline testing or scenarios where internet connectivity is limited.

Limited offline testing


Rest Assured

REST-Assured is a Java-based DSL (Domain Specific Language) that lets you write readable and powerful tests for RESTful APIs (not for SOAP APIs). As a Java library, it easily integrates with Junit, TestNG, or other Java frameworks and quickly fits into CI/CD processes. The code is human-readable as it supports the Given-when-then notation, similar to if-else statements.

REST-Assured uses a declarative syntax that is expressive and easy to read. This makes it accessible to developers and testers, allowing them to write tests in a natural and readable manner.

Declarative syntax

REST-Assured is a Java library that seamlessly integrates with Java-based projects.

Integration with Java

REST-Assured supports a BDD approach to test writing, allowing users to describe test scenarios in a natural language format. This is achieved through the use of Given-When-Then syntax.

Support of the BDD approach

REST Assured supports various authentication mechanisms, including basic authentication, OAuth, and API key authentication. This is crucial for testing APIs that require secure access.

Authentication support

Setting up REST Assured for API testing is relatively straightforward and requires minimal configuration. This simplicity can be beneficial for getting started quickly.

Easy to Set Up

While REST-Assured provides much built-in functionality for common use cases, it is also extensible, allowing users to implement custom logic or integrate it with other libraries when needed.



As a Java library, REST-Assured is suitable for Java projects. Teams working with other programming languages may need to use alternative tools.

Java dependency

For small projects with simple testing requirements, using a full-fledged Java library like REST-Assured might be considered overkill, and more straightforward tools or frameworks could be more appropriate.

Overkill for small projects



Karate is an open-source tool that combines API testing, test automation, and performance testing into a single framework. It is designed to simplify API testing using a simple syntax based on the Gherkin language.

Karate uses a BDD syntax that is easy to read and write, making it accessible to technical and non-technical team members.

BDD syntax

Karate supports data-driven testing, allowing users to easily parameterize and vary test scenarios based on different data sets.

Data-driven testing

While Karate itself is primarily based on the Java Virtual Machine (JVM), it allows the inclusion of JavaScript for scripting purposes, providing flexibility for users with JavaScript expertise.

JavaScript integration

One of the notable strengths of Karate is its approach to minimizing the amount of boilerplate code needed for API testing. It aims to make testing accessible to non-programmers while still providing powerful capabilities for technical users.

No coding required

Karate can handle API and performance testing within the same framework, reducing the need for separate tools for different testing phases.


Karate generates detailed HTML reports that include information on test results, scenarios, and timelines, aiding in the analysis of test execution results.

Detailed test reports


While Karate has gained popularity, it may not have as extensive a community or ecosystem as some other testing tools, which could result in fewer resources and third-party integrations.

Limited ecosystem and community support

Compared to general-purpose programming languages, Karate might be less extensible for implementing custom functionality or integrations beyond its built-in capabilities.

Less extensible

Karate is built on the JVM, which might be a limitation for teams that prefer or primarily work with other programming languages or platforms.

Java dependency



Paw is a powerful API testing and development tool designed for macOS. It provides a user-friendly interface for developing, testing, and debugging APIs. This tool allows businesses to check APIs, make requests, create client code, and save API details, among other tasks. Paw makes teamwork easier by letting users sync their tests. This way, everyone can make changes without conflicts and see real-time updates.

Paw supports using dynamic values and environments, allowing users to create flexible requests that adapt to different scenarios. This is useful for handling authentication tokens, variables, and dynamic data.

Dynamic values and environments

Paw can generate code snippets in various programming languages based on the configured API requests. This feature accelerates the development process by providing developers with ready-to-use code.

Code generation

Paw supports using environment variables and configurations, enabling users to define and manage different parameters for testing in various environments.

Environment variables and configurations

Paw supports importing and exporting API requests and configurations, facilitating collaboration, and sharing test cases among team members.

Import and export


Paw is available only for macOS, which limits its usability for users on other operating systems.

macOS exclusive

Paw is a commercial tool, and while it offers a free trial, a paid license is required for full access to its features.

Paid software


Apache JMeter

JMeter is used for various types of testing, including load, functional, and unit testing. Its primary application is for web applications but it can also be used for basic performance monitoring. JMeter supports numerous protocols and servers, such as HTTP, HTTPS, SOAP, LDAP, FTP, etc. It is open-source and available for free. Finally, JMeter has an interactive and user-friendly interface, making it easy to use.

Apache JMeter excels in performance testing and is widely used for simulating multiple users to test the performance and scalability of web applications, including APIs.

Performance testing

JMeter supports distributed testing, allowing users to scale their tests across multiple machines to simulate a larger number of virtual users and increase testing capacity.

Distributed testing

JMeter supports many protocols, including HTTP, HTTPS, FTP, SOAP, REST, LDAP, JDBC, and more. This versatility makes it suitable for testing various types of applications, including APIs.

Rich set of protocols

JMeter is extensible and allows users to create custom plugins and functions to meet specific testing requirements. There is an active community that contributes to the development of plugins.



While JMeter provides basic reporting and graphing features, it may not have the sophisticated reporting capabilities of some commercial performance testing tools.

Limited reporting

Individual testers often use JMeter, and its collaboration features may not be as robust as those in some other testing tools designed for team environments.

Limited collaboration features



RestSharp is a popular open-source library for working with RESTful APIs in .NET applications. RestSharp simplifies making HTTP requests and handling responses, making it easier for developers to interact with RESTful APIs in their .NET projects.

RestSharp is designed with RESTful principles, allowing developers to work seamlessly with RESTful APIs. It supports standard HTTP methods like GET, POST, PUT, DELETE, etc.

Support for RESTful principles

RestSharp includes built-in support for serializing and deserializing JSON and XML data. This simplifies working with complex data structures when communicating with RESTful APIs.

Serialization and deserialization

RestSharp supports various authentication mechanisms, including OAuth, making it versatile for interacting with APIs that require authentication.

Authentication support

RestSharp allows developers to make asynchronous HTTP requests, improving the performance of applications that handle multiple requests simultaneously.

Asynchronous support


RestSharp's documentation may not be as extensive or detailed as some other tools, and users might need to rely on community resources or trial and error to address specific use cases.

Limited built-in documentation

RestSharp is a library that needs to be integrated into a .NET application. As such, it doesn't provide a standalone user interface or test runner like some dedicated API testing tools.

Not a standalone tool

The development and maintenance of RestSharp might depend on the activity of the open-source community. If updates are infrequent, it could potentially lack support for the latest features and security updates.

Updates and maintenance


Charles Proxy

Charles Proxy is a web debugging proxy application commonly used by developers, testers, and network administrators. It allows users to monitor, inspect, and manipulate network traffic between a computer or mobile device and the internet. Charles Proxy is widely used for various purposes, including monitoring and testing API requests and responses.

Charles Proxy provides a detailed view of HTTP and HTTPS traffic, allowing users to inspect headers, bodies, and other parameters. This helps debug and understand the communication between a client and a server.

Traffic monitoring and inspection

Developers can set breakpoints to intercept and inspect requests and responses. This feature is valuable for debugging and analyzing how an application interacts with a server.


Charles Proxy supports SSL proxying, allowing users to inspect encrypted HTTPS traffic by acting as a man-in-the-middle. This is beneficial for debugging secure connections.

SSL proxying

It allows users to simulate different network conditions by throttling the bandwidth. This is useful for testing how an application performs under varying network speeds.

Bandwidth throttling


Charles Proxy may be overwhelming for beginners, especially those new to network debugging.

Complexity for beginners

While there is a free version of Charles Proxy with limited features, the full version has a price tag. Depending on the user's needs, the cost may be a consideration.




Katalon Studio is a framework for automating the testing of APIs and web, mobile, and desktop applications. It has rich features and can run on Windows, macOS, and Linux platforms.

Katalon Studio has a user-friendly interface, making it accessible for testers with varying experience levels, including those who may not be proficient in programming.

Low learning curve

Katalon Studio supports BDD by integrating tools like Cucumber and Gherkin, enabling collaboration between developers, testers, and other stakeholders.

Behavior-driven development (BDD)

Katalon Studio includes a built-in object repository for managing test objects enhancing test maintenance and reusability.

Object repository

Katalon Studio offers features for organizing and managing test cases, making it easier for teams to maintain and scale their test suites.

Test case management

Katalon Studio can integrate with popular version control systems like Git, facilitating collaboration and versioning of test scripts.

Version control

Katalon Studio provides built-in reporting features, offering insights into test execution results.

Test reporting


While Katalon Studio supports scripting in Groovy, some users prefer more commonly used programming languages like Java or Python. Groovy, while powerful, may have a steeper learning curve for some users.

Scripting language

While Katalon Studio is suitable for many testing scenarios out of the box, more advanced customization options might be limited compared to tools with a more open architecture.

Advanced customization

Katalon Studio's pricing model may not be suitable for all organizations, especially for smaller teams or individual testers with budget constraints.

Pricing structure



Insomnia is a simple and user-friendly tool for testing and debugging APIs. It enables you to send requests, view responses, and analyze errors. Insomnia supports a broad range of capabilities for interacting with various APIs: a set of HTTP/s methods, calls to gRPC APIs, as well as custom methods with their parameters. There are also many options for message formats, including JSON, XML, YAML, EDN, binary files, and GraphQL Queries.

Insomnia is available on multiple platforms, including Windows, macOS, and Linux, making it accessible to many developers.

Multiple platforms

Users can easily create HTTP requests with various methods (GET, POST, etc.) and customize headers, parameters, and body content.

Flexible request building

Insomnia allows users to generate code snippets in various programming languages based on the requests they create, facilitating integration with code projects.

Code generation

Insomnia features a plugin system that allows users to extend its functionality, integrating additional tools or customizing their workflow.



While Insomnia excels in testing RESTful APIs, it might not be the best choice for projects heavily reliant on other protocols like SOAP.

Focused on REST

While Insomnia has an active community, it might not be as extensive as some API testing tools, potentially resulting in fewer third-party plugins and extensions.

Community size

Insomnia primarily focuses on creating and testing individual requests and responses and may lack some of the advanced testing features found in more comprehensive testing tools.

Focused on request/response

Insomnia may not have all the features needed for large-scale enterprise API testing, which might lead organizations to consider more comprehensive solutions for complex testing scenarios.

Enterprise-level features



SoapUI is a cross-platform, open-source API testing tool that allows testers to perform automated regression, functional, load, security, and compliance testing. It supports API testing because SoapUI is compatible with standard protocols such as SOAP/WSDL, JMS, REST, AMF, JDBC, etc.

SoapUI supports both SOAP and REST, making it suitable for testing a wide variety of web services.

Support for multiple protocols

Its user-friendly interface allows both beginners and experienced testers to create and execute tests efficiently.

Intuitive interface

The support for data-driven testing allows testers to cover various scenarios with different input data.

Flexible data handling

SoapUI can be extended through plugins and custom scripts, enabling users to tailor it to specific needs.

Extensions and plugins


While SoapUI is easy to start with, some of its more advanced features might have a steeper learning curve.

Complex features

Running extensive test suites or load tests can be resource-intensive, impacting system performance.

Resource usage

Advanced features, such as security and load testing, are often part of the Pro version, which comes with a cost.

Pro version features



Swagger, now known as the OpenAPI Specification, is not an API testing tool per se; instead, it is a framework for describing RESTful APIs. However, it is often associated with API testing due to its ability to automatically generate documentation and client SDKs based on the API specification.

OpenAPI Specification is widely adopted and supported, promoting interoperability between tools and frameworks.

Open standard

Many enterprises use and support OpenAPI. It's like a collection of their knowledge from building many APIs over the years.

Huge user base

Generating client libraries in various languages reduces the effort developers need to use the API.

Client libraries


For those new to API specification and documentation tools, a learning curve may be associated with understanding and using OpenAPI effectively.


Using OpenAPI may be seen as overkill for small, simple APIs, adding unnecessary complexity.




Postman simplifies API testing and quickly integrates it into the CI/CD pipeline, allowing for accelerated development, testing, and monitoring. The Postman API development environment consists of collections, built-in tools, and workspaces. You can execute requests, debug, test, create, and document simulation scenarios, as well as monitor APIs. Collections can be shared, permissions can be assigned, and collaboration with colleagues in a shared space is possible.

Postman is versatile and can be used for various aspects of API development, including testing, debugging, and monitoring.


A large community around Postman and extensive documentation make it easier for users to find support and learn from others.

Community and documentation

Postman integrates well with other development tools and services, making it a valuable part of the development workflow.


Postman receives regular updates and improvements, ensuring relevance to evolving technologies.

Regular updates

The basic pricing plan is free and includes all necessary features for teams of various sizes.

Free basic plan


Postman can be resource-intensive, especially for extensive API collections or complex test scenarios, affecting performance on less powerful machines.

Resource intensive

Some developers prefer command-line tools, and Postman's heavy reliance on a graphical interface may not cater to everyone's preferences.

Dependency on a GUI

The free version has limitations on the number of requests, monitoring, and other advanced features.

Limited free tier


This challenge is choosing the right automated API testing tools. The modern, ever-changing IT market offers a myriad of them. On the one hand, it helps companies streamline the testing lifecycle, enhance test coverage, and contribute to the overall success of your software development projects. But on the other hand, it turns the choosing process into a real challenge and increases the chance of making mistakes.

For over 18 years, the byVoice team has been specializing in testing APIs. Based on this experience, we gathered our TOP 12 API automation testing tools and highlighted their features, pros, and cons to make your choice easier.

API Testing Challenge That Requires Special Attention

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Find Out How We Helped Our Customers Succeed with Test Automation

Speed and efficiency: Automation allows for fast test scenario execution, significantly reducing the testing lifecycle. This rapid feedback loop is crucial, especially in agile development environments, to identify and address potential issues promptly.


CI/CD pipelines: Implementing automated tests into these pipelines enables a seamless and streamlined development workflow. This integration ensures that each code change undergoes rigorous testing automatically, preventing the introduction of defects into the software and promoting a more reliable and stable codebase.


Better coverage: Automated tests can cover a wide range of scenarios, edge cases, and input variations, helping to identify potential issues that might be overlooked in manual testing. This comprehensive test coverage contributes to the overall reliability and robustness of the API.


Software validation: API testing provides complete software validation by extending its capabilities to acceptance and load testing. In acceptance testing, automated scripts can simulate real user interactions, validating that the API functions as expected in various scenarios. Load testing allows developers to assess the system's performance under varying stress levels and concurrent usage.


Handling complex and repetitive tasks: APIs often involve intricate interactions, and automated tests consistently replicate these interactions. This reduces the likelihood of human errors and ensures that all aspects of the API functionality are thoroughly examined.


Both manual and automated approaches are available for API testing. However, automated testing offers several benefits over the manual one, making it a preferred choice.

To Automate, or Not to Automate, That is the Question

APIs need to run a marathon without tripping when testing the performance under various conditions, such as high load or concurrent requests. Identifying and resolving bottlenecks in API performance is critical for ensuring scalability.

Performance testing

APIs must return appropriate error responses in case of invalid requests or unexpected situations. Handling and reporting errors in a clear and user-friendly manner is a challenge.

Error handling

Despite the crucial role automation plays in enhancing API testing efficiency, the creation and upkeep of automated scripts pose formidable challenges. The fluid nature of APIs, dynamic data, and evolving requirements introduces complexities that demand adept handling to ensure the sustained effectiveness of automated testing processes.

Automation challenges

Security concerns

Challenges in this area include the following:

Handling authentication tokens

Securing sensitive data in transit

Protecting against common security threats like SQL injection or cross-site scripting

It looks like a digital James Bond mission, doesn’t it?

Setting up a suitable test environment that mirrors the production one is like building a house of cards, especially if the API relies on third-party services or external dependencies. You are stacking each card carefully, hoping that the slightest breeze (or API hiccup) doesn't make your carefully crafted structure tumble.

Test environment setup

Handling different data types is much like attempting to juggle multiple fruits simultaneously. Just as juggling requires a keen sense of coordination, handling data variety demands a thorough approach to ensure nothing gets dropped or mixed up.

Data management

APIs may depend on external services, and testing these dependencies can be challenging. Network issues, service downtimes, or changes in third-party APIs can impact the reliability of API tests.

Dependency on external systems

The reality turns out to be harsh. In software development, where seamless communication between components is crucial, the journey of API testing unfolds with multiple challenges.

Where can you step on a rake?

Sounds Сool, But How Does It Work in Practice?

Moreover, public API can help our customers expand their market reach. The client offers a public API integrating with CRM platforms and third-party services that attract a broader customer base. The enhanced capabilities and seamless integrations positioned the client as a leader in the telecommunications industry, leading to increased adoption and market share.

When using APIs, a high level of consistency is one of the most crucial aspects. This makes the development process predictable and ensures users can continue integrating their software with existing programs without changing their operations. Seeking such a level of quality involves the use of API testing processes.

This process is crucial because various parts of applications are generally not tightly connected. At the same time, APIs reside in the business layer, which constantly changes. By utilizing API testing tools, any alterations in the request/response format or within the API itself can be identified in the early stages of testing. This streamlines the integration and regression testing phases, leading to a reduction in the software testing lifecycle.

Fun fact: APIs make up over 83% of Internet traffic. They assist in creating omnichannel experiences, expediting innovation, enhancing business efficiency, and generating new revenue streams.

Every day, we use applications on our phones, work on the internet through a browser, make purchases using bank cards, and perform numerous other actions with electronic gadgets that communicate with each other through APIs.

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