API Testing Tools

Organisations in the United Kingdom are turning to APIs to integrate their applications with third-party apps. An application programming interface (API) is a set of rules and protocols that allows different software systems to communicate, while application programming interfaces enable scalable and efficient data transfer and system integration. Thus, API testing is expected to be essential in software development, now and in the future. API Testing Tools focuses on validating APIs‘’ functionality, performance, security, and reliability. The process also involves testing for compatibility with various browsers and devices.

As APIs become increasingly complex regarding features and functionality, testers in the UK must develop sophisticated test plans that cover all aspects of the API. The use of API testing automation tools is also expected to increase significantly in the coming years.Effective API design and well-defined API specifications, such as those using OpenAPI or GraphQL, are crucial for building robust and maintainable APIs.

The use of API testing automation tools is also expected to increase significantly in the coming years. Automated tests help reduce manual effort and improve test case coverage by running tests quickly across multiple environments. API testing tools also help detect errors earlier in the development process, reducing costs associated with fixing bugs later in the cycle. Integrating API testing throughout the development lifecycle ensures quality and reliability at every stage.

Benefits of API Testing in Agile

API testing is an essential part of agile software development. It helps to ensure that the application is functioning as expected and allows developers to detect any issues that may arise during development quickly. Here are some key benefits of API testing in an agile environment:

Promotes Automation:

API testing is an ideal candidate for automation, saving manual testing time and effort. Automated tests can be run more frequently, allowing for faster feedback and quick fixes to any issues that may arise.

Improves Quality:

By testing APIs early and often, developers can quickly identify problems before they become significant issues. This helps to ensure a higher quality product is delivered on time and within budget.

Quickens Dev Cycles:

By running automated tests regularly, the Dev team can reduce the amount of time needed for debugging and bug fixing, resulting in shorter development cycles. This also helps to reduce costs associated with rework or delays due to bugs or compatibility issues.

Increases Team Collaboration:

API testing encourages collaboration between different teams, such as testers, developers, and operations personnel, who all need to work together to deliver a successful product on time.

Thorough Testing Coverage:

API testing provides comprehensive coverage of the application’s functionality and performance which helps to ensure that all areas of the system are tested thoroughly before it goes live.

Data Driven Testing:

Data-driven testing in API testing is a technique that involves using various sets of test data to validate the functionality, performance, and reliability of an API. With data-driven testing, testers can create multiple test cases that cover different scenarios and variations, allowing for more comprehensive test coverage.

Key Features to Look for in an API Testing Tool

Automated Testing:

API testing tool should be able to automate the testing process, allowing you to quickly and efficiently test your APIs. Automation helps reduce the time and money spent on manual testing, allowing you to focus on other aspects of product development.

Comprehensive Reporting:

A good API testing tool should provide extensive reporting capabilities that allow you to quickly analyze the results of your tests and identify any potential issues or areas of improvement. This will enable you to make informed decisions about improving your APIs.

Cross-Platform Support:

As more applications move towards a multi-platform approach, an API testing tool must support multiple platforms, including web, mobile, and cloud-based services. This ensures that your APIs are tested across all platforms and can work seamlessly with other services and products.

Security Testing:

Security is an essential part of any application or API service, so an API testing tool needs to include security tests in its suite of features. These tests should ensure that the APIs are secure from malicious attacks and protect user data from unauthorised access or manipulation.

Ease of Integration:

The best testing API tools should be easy to integrate with existing systems and processes, allowing developers to quickly set up tests without having to learn a complex new language or system architecture. This makes it easier for developers to start their projects quickly and ensure that their APIs are appropriately tested before launch.

Non-technical Friendly:

The API testing tools’ documentation should feature support for BDD conventions, enabling even the non-tech-savvy stakeholders to understand the project details via easy-to-understand reports.

Top 10 API Testing Tools in the Software Testing Industry

The following are some of the tools for testing API that QA engineers use:

Katalon Studio

Katalon Studio is an automated testing platform that helps users create comprehensive end-to-end tests quickly and easily with its integrated environment for API, Web UI, mobile app testing, and cross-browser compatibility testing.

Key Features:  

• Supports SOAP and RESTful requests  

• Reusable scripts across projects  

• Visual test flow and codeless execution  

• CI/CD integrations  

Limitations:  

• Desktop-only application (not browser-based)  

• Advanced features are locked behind the enterprise plan  

Tricentis Tosca

Tricentis Tosca is an enterprise-level API test automation solution designed to help users create reliable tests faster than ever before by taking advantage of model-based test automation technology combined with AI-powered analytics capabilities.

Key Features:  

• Model-based test automation  

• Built-in support for SOAP, REST, JMS, and other protocols  

• AI-powered test case design  

• Strong versioning and test case reuse  

Limitations:  

• High learning curve for beginners  

• Premium pricing for full capabilities  

Postman

Postman is a popular tool that automates API testing. It is one of the API loading testing tools that allow users to easily create complex requests, save them for reuse, and share them with others. It also includes features such as automated tests, response data validation, environment variables, and more.

Key Features:  

• Create and automate test requests quickly  

• Collection runner for batch tests  

• Integrated monitoring and mocking  

• Public and private API workspaces  

Limitations:  

• Limited load testing features  

• Not ideal for complex workflows or test orchestration  

SoapUI

It is an open-source web service testing tool ideal for service-oriented architectures (SOA) and representational state transfers (REST services). It provides complete test coverage, from functional to security testing, and supports all major protocols, including SOAP/WSDL, REST/JSON, and GraphQL.

Key Features:  

• Complete testing support for SOAP, REST, and GraphQL  

• Data-driven testing with external files  

• Groovy scripting support  

• Security and performance testing modules  

Limitations:  

• The interface can feel outdated  

• Needs scripting skills for complex tests

Apache JMeter

Apache JMeter is an open-source load and performance testing tool used to analyse the performance of web applications under various load types. It can be used to simulate a heavy load on a server or network to test its strength or analyse overall performance testing under different load types.  

Key Features:  

• High scalability for simulating users  

• Supports HTTP, HTTPS, SOAP, REST, FTP, JDBC  

• Graphical reporting and dashboarding  

• Extensible via plugins  

Limitations:  

• Not purpose-built for functional API testing  

• UI may overwhelm non-technical users

Parasoft SOAtest

Parasoft SOAtest is an automated and open-source API testing tool designed to help organisations ensure the quality of their services through comprehensive functional, security, performance, regression & compliance tests across multiple environments & protocols with minimal effort & cost associated with manual QA processes.

Key Features:  

• Supports end-to-end testing across REST, SOAP, MQ, and JMS  

• Service virtualization support  

• Integration with CI/CD pipelines  

• Built-in AI-powered test generation  

Limitations:  

• Requires initial setup and training  

• Expensive for small teams  

Rest Assured

Rest Assured is an open-source Java library that can be used to automate RESTful Web Services using JSON or XML payloads to perform functional validation on the response received from the server-side application over the HTTP protocol(s), including secure HTTPS requests.

Key Features:  

• Simple syntax for REST calls  

• Supports XML and JSON payloads  

• Can be integrated with JUnit/TestNG  

• Ideal for behaviour-driven development (BDD)  

Limitations:  

• Java-specific (not for other language stacks)  
• No GUI, strictly code-driven  

Apigee

Apigee is a cross-cloud API platform that enables developers to quickly design, deploy, secure, monitor, analyse and scale APIs. The platform provides tools for debugging, mocking, traffic management, quota management, analytics, etc.

Key Features:  

• Real-time analytics and monitoring  

• Developer portal integrations  

• Built-in security and quota policies  

• CI/CD integration  

Limitations:  

• More focused on API management than testing  

• Complex pricing structure  

Runscope

Runscope provides a suite of API monitoring tools that allow developers to check uptime and performance metrics like latency & throughput as well as run end–to–end API tests. The tool also allows teams to collaborate on API development & troubleshooting.

Key Features:  

• Intuitive dashboard with test scheduling  

• Alerts for downtime and latency  

• Tests from multiple global locations  

• Slack and webhook integrations  

Limitations:  

• Limited support for SOAP APIs  

• No load or performance testing  

Assertible

Assertible provides continuous integration & deployment tools designed explicitly for API tests. The platform allows users to set up automated integration & regression tests which can then be monitored in real-time using dashboards & alerts.

Key Features:  

• Easy user interface  

• Assertions and validations via the dashboard  

• CI/CD pipeline integrations  

• Real-time status monitoring  

Limitations:  

• Basic features in the free plan  

• Limited customisation in test logic  

AI-Powered Features in API Testing Tools  

As APIs continue to evolve in complexity and scale, leading testing tools are adopting AI to enhance reliability, speed, and test coverage. Here’s how some of the top tools are bringing AI into play:  

Postman  

Postman has started integrating AI-driven features like:  

• Auto-generated test scripts based on API responses  

• AI-based code suggestions for test assertions  

• Smart test creation using behaviour prediction  

• AI chatbot for test writing assistance (in beta)  

Katalon Studio  

Katalon’s new Smart Test Generator and AI-powered analytics help in:  

• Auto-generating test cases from Swagger/OpenAPI schemas  

• Self-healing test objects to maintain test stability across UI/API changes  

• AI-based test prioritisation using historical test data  

• TestOps dashboard with predictive analytics  

Swagger/OpenAI/Stoplight (SwaggerHub)  

While Swagger by itself is more of a documentation-first framework, tools like SwaggerHub and integrations with OpenAI and Stoplight add AI-backed capabilities:  

• Schema-driven test generation  

• AI-assisted mock server creation  

• Smart documentation with contextual hints  

• Natural language API descriptions turned into tests 

How Does AI Impact the API Testing Process 

Integrating AI into I testing isn’t just about automation. It’s about building smarter, resilient testing strategies that align with agileAP and DevOps pipelines. Here’s what AI brings to the table:  

Reduced Manual Effort  

AI can auto-generate test scripts, suggest assertions, and even self-heal broken test flows. This saves hours of manual intervention during updates or sprint changes.  

Faster Release Cycles  

With predictive test execution, intelligent prioritisation, and auto-maintenance of test cases, teams can accelerate their test cycles and reduce time-to-market significantly.  

Smarter Test Coverage  

AI helps identify critical paths, data gaps, and under-tested areas. This can lead to wider test coverage and less production surprises.  

Conclusion

API testing has become an essential part of software development in the United Kingdom and is expected to continue to grow in importance beyond 2025. It involves conducting performance, security, reliability, and functionality testing of APIs and their compatibility with various browsers and devices.

Today, the advancement of technology has led to apps becoming more complex in their architecture, featuring multiple layers. To ensure that these apps function correctly and provide a positive customer experience (CX), API testing must be conducted to validate different business layers to guarantee seamless applications. Digital businesses should seek services from next-gen testing service providers for fully functional business applications.

How Can TX Help Digital Businesses with API Testing?

TestingXperts (Tx) is one of the fifth-largest global pure-play software testing services providers. TX has been chosen as a trusted QA partner by Fortune companies and ensures superior testing outcomes for its global clientele. We have rich expertise in enabling end-to-end API testing services for international clients across various industry domains like healthcare, telecom, BFSI, retail & eCommerce, etc.

API Testing Services Offered

Unit testing

Utilised to check the functionality of individual APIs.

Functional testing

Employed to test end-to-end functionality of the API layer.

Load testing

Validates both functionality and performance for the system under various levels of user/transaction load.

Runtime error detection

Involves executing automated or manual tests to identify problems, such as exceptions and resource leaks.

Security testing

Includes a variety of security checks, such as penetration testing, authentication, encryption, and access control.

Web UI testing

Entails end-to-end testing of the entire system using APIs.

Contract testing

Used to check the interaction between client and API or server and to verify data exchanges between two parties.

Why Choose Testingxperts for API Testing Services

• TestingXperts is a Katalon Solution Partner Program member, enabling clients to deliver high-quality software faster by leveraging comprehensive DevOps and testing practices.

• Team of expert API testers with expertise in various protocols, including XML, SOAP, JSON, REST, Gdata, YAML, ATOM, RSS and RDF.

• QA engineers experienced in performing end-to-end application validations at all application levels.

• Certified team with extensive knowledge of code-level functionalities to ensure high test accuracy.

• Hands-on experience with industry-leading open source and commercial.

• Our custom test execution report provides stakeholders with a rich interface for easy access to results. Lastly, we partner with renowned organisations such as UiPath, Tricentis, AccelQ, EggPlant, and more.