APIs are the hidden connectors behind almost every piece of modern software. When one breaks, it can throw your whole system off balance. That’s why having a testing partner who really gets APIs is so important. Across the UK, there are companies doing a great job of combining tech know-how with practical problem-solving. Whether you’re rolling out a new product or keeping a complex system running, the right team can save you time, money, and plenty of headaches.
1. A-Listware
At A-listware, we provide software development and IT consulting services with a strong connection to the UK, working across industries like FinTech, healthcare, and retail. We build and manage teams that integrate directly with our clients’ operations, making collaboration straightforward and keeping projects moving efficiently. By combining technical expertise with flexible management, we handle challenges and shifting priorities without losing momentum.
Our UK teams are supported by local leaders who guide communication and workflow, ensuring that every project meets our clients’ needs. We leverage a wide pool of skilled professionals to deliver consistent results in software development, API testing, infrastructure management, and more. Our goal is to make our teams feel like an extension of our clients’ own staff, keeping operations smooth and reliable.
Key Highlights:
- End-to-end software development and IT consulting
- Direct integration of teams with client operations
- Local UK leadership for clear communication and guidance
- Flexible team management with low staff turnover
- Expertise across multiple industries and technologies
Services:
- API testing and quality assurance
- Software development outsourcing
- Team augmentation and management
- Cloud and on-premises infrastructure support
- UI/UX design, DevOps, and cybersecurity services
Contact Information:
- Веб-сайт: a-listware.com
- Електронна пошта: info@a-listware.com
- Фейсбук: www.facebook.com/alistware
- LinkedIn: www.linkedin.com/company/a-listware
- Address: St. Leonards-On-Sea, TN37 7TA, UK
- Phone Number: +44 (0)142 439 01 40
2. KiwiQA
KiwiQA focuses on software testing and QA in the UK. They cover both manual and automated testing, making sure issues are caught quickly and reported clearly. Their teams plan and execute projects efficiently, helping clients keep software running smoothly.
They combine years of experience with modern tools, adapting to each client’s needs. The result? Accurate testing that fits your schedule and gives actionable insights. Their work spans multiple industries, so software performs reliably under all sorts of conditions.
Key Highlights:
- Expertise in both manual and automated testing
- Structured approach to planning and execution
- Communication of findings through clear reporting
- Use of modern tools and testing techniques
- Experience across multiple industries and project types
Services:
- API testing and quality assurance
- Manual software testing
- Automated software testing
- Mobile app testing
- Security testing
- Software test consulting
Contact Information:
- Website: kiwiqa.co.uk
- E-mail: sales@kiwiqa.com
- Facebook: www.facebook.com/kiwiqaservicesptyltd
- Twitter: x.com/KQSPL
- LinkedIn: www.linkedin.com/company/kiwiqa-services
- Address: Vista Business Centre 50 Salisbury rd Hounslow TW4 6JQ United Kingdom
- Phone: +61 472 869 800
3. AscentiQ Solutions
AscentiQ Solutions works across the UK, serving sectors like finance, healthcare, and public services. They integrate testing into whatever development workflow you’re using – Agile, Waterfall, or Rapid – so quality stays consistent. Their focus is on catching issues early, which reduces risk and keeps delivery smooth.
They mix hands-on testing methods with domain expertise. Manual, automated, API, accessibility, or user acceptance testing – they tailor the approach to what the client actually needs. The goal is always clear insights and software that works as intended.
Key Highlights:
- Independent UK-based software testing team
- Integration with Agile and traditional development workflows
- Focus on early defect detection and risk reduction
- Tailored testing strategies based on client needs
- Expertise across multiple industry sectors
Services:
- API testing
- Web application testing
- Mobile app testing
- Test automation
- User acceptance testing
- Accessibility testing
- Risk-based testing
- Product and project-based testing
Contact Information:
- Website: ascentiqsolutions.co.uk
- E-mail: sales@ascentiqsolutions.co.uk
- Facebook: www.facebook.com/Ascentiq-Solutions-1622336601313319
- Twitter: x.com/AscentIQ_
- LinkedIn: www.linkedin.com/company/ascentiq-solutions
- Address: Office T31 103 Cranbrook Road, Ilford, London, IG1 4PU
- Phone: 020 3435 6842
4. Sogeti
Sogeti, part of the Capgemini group, brings technology services to UK clients with a practical, collaborative approach. They focus on integrating quality engineering and software testing throughout development projects, applying agile practices and the latest tech to make sure everything works reliably.
Their teams understand client systems deeply and adjust testing accordingly. From API testing to automation and user experience checks, they combine local expertise with global know-how. The goal is simple: help organizations improve software quality while keeping processes smooth and structured.
Key Highlights:
- UK-based teams with agile and local integration
- Emphasis on quality engineering and process-driven testing
- Combines global knowledge with local client understanding
- Focus on practical, goal-oriented testing solutions
- Supports multiple sectors with structured testing approaches
Services:
- API testing
- Test automation
- Functional and non-functional testing
- User experience testing
- Quality engineering consulting
- Software verification and validation
- Agile and DevOps testing support
Contact Information:
- Website: www.sogeti.com
- LinkedIn: www.linkedin.com/company/sogeti
- Address: 95 Queen Victoria St, London, EC4V 4HN
5. AtheosTech
AtheosTech is a digital consultancy in the UK that focuses on understanding client systems before diving into testing. Their goal is to make sure APIs and software components function properly without unnecessary complications. They also integrate testing into broader development cycles to keep things traceable and reliable.
Whether it’s web or mobile apps, manual or automated testing, their teams analyze systems and prioritize potential issues, giving clients practical insights into software performance. They adapt to client-specific requirements, making sure testing aligns with how the software is actually developed and used.
Key Highlights:
- UK-based teams with focus on client system understanding
- Integrates testing with broader software development cycles
- Emphasis on structured processes and traceability
- Supports a variety of industries and application types
- Uses both manual and automated testing approaches
Services:
- API testing
- Manual and automated testing
- Web and mobile application testing
- Functional and non-functional testing
- Software validation and verification
- System analysis and risk assessment
- Client-specific testing workflows
Contact Information:
- Website: atheostech.com
- E-mail: contact@atheostech.com
- Facebook: www.facebook.com/atheostech
- Twitter: x.com/AtheosTech
- LinkedIn: www.linkedin.com/company/atheostech
- Instagram: www.instagram.com/atheostechofficial
- Address: RK World Tower, 728, 150 Feet Ring Rd, Shastri Nagar, Dharam Nagar Society, Rajkot, Gujarat 360007, India
- Phone: +91-63525-51072
6. IBN Technologies
IBN Technologies provides IT solutions and outsourcing, with a focus on software development, integration, and testing. Their teams analyze business processes to create testing strategies that fit each client. When it comes to API testing, they focus on validation, functional checks, and automation to keep software reliable.
They also offer IT consulting and process automation, blending domain knowledge with technical expertise. Their approach is flexible, adapting to the unique needs of each software environment, while still following structured methodologies.
Key Highlights:
- Global delivery with teams in the UK, USA, and India
- Integrates testing with development and business processes
- Focus on automation and functional validation
- Supports diverse industries and IT environments
- Combines consulting, software development, and testing expertise
Services:
- API testing
- Custom software development
- Integration services
- IT consulting
- Хмарні сервіси
- Intelligent process automation
- Risk and process analysis
Contact Information:
- Website: www.ibntech.com
- E-mail: sales@ibntech.com
- Facebook: www.facebook.com/ibntechnologies
- Twitter: x.com/IBNTechnology
- LinkedIn: www.linkedin.com/company/ibn-technologies-limited
- Instagram: www.instagram.com/ibntechnologies
- Address: 30 Orange Street, London UK WC2H 7HF
- Phone: +44-800-041-8618
7. QATestLab
QATestLab is all about helping companies get their software quality on point. They don’t just dive in blindly – they take a good look at how your testing is set up, what tools you’re using, and how ready your QA team really is. When it comes to API testing, they focus on making sure everything works like it should, spotting risks early, and streamlining processes to keep things running smoothly.
On top of that, they run workshops and online sessions to get your QA teams up to speed. It’s a mix of hands-on guidance and practical advice, aimed at cutting risks, boosting transparency, and making sure projects stay on track without compromising quality.
Key Highlights:
- Independent evaluation of QA processes
- Focus on testing efficiency and risk reduction
- Training for QA teams and project managers
- Recommendations for process improvements
- Support for documentation and compliance
Services:
- QA consulting
- Testing process assessment
- API testing support
- Test plan and strategy review
- QA team training
- Process optimization
- Automation assessment
Contact Information:
- Website: qatestlab.com
- E-mail: contact@qa-testlab.com
- Facebook: www.facebook.com/qatestlab
- Twitter: x.com/QATestLab
- LinkedIn: www.linkedin.com/company/qatestlab
- Address: 34 Falirou Street, 1st Floor, Office 115 2066 Strovolos, Nicosia, Cyprus
- Phone: +357 22 27-04-66
8. Zoonou
Zoonou is an employee-owned QA and software testing company in the UK. They take a really practical approach: checking your current QA strategy, running thorough tests for performance, security, and accessibility, and helping teams fix any gaps. With API testing, they make sure processes are smooth, risks are managed, and systems behave reliably.
They also offer consulting and automation support, helping teams apply modern QA methods and stay productive. It’s a mix of strategic thinking and hands-on testing, aimed at keeping QA processes flexible but crystal clear, so projects move along without surprises.
Key Highlights:
- Independent and objective QA assessments
- Emphasis on accessibility and usability
- Flexible delivery models for varied project needs
- Support for process improvements and documentation
- Guidance on QA strategy and team structure
Services:
- API testing and software quality assurance
- Performance and load testing
- Test automation implementation
- Digital accessibility testing
- Cyber security assessment
- QA strategy consulting
- Test process optimization
Contact Information:
- Website: zoonou.com
- E-mail: info@zoonou.com
- LinkedIn: www.linkedin.com/company/zoonou
- Instagram: www.instagram.com/zoonou
- Address: Suite 1, The Workshop 10-12 St Leonards Road Eastbourne, East Sussex BN21 3UH
- Phone: +44 (0) 1323 433 700
9. Belitsoft
Belitsoft is more than just a testing company – they do full-cycle development too. Their teams handle backend, frontend, cloud, and API work, while making sure everything is tested properly along the way. In API testing, they focus on keeping things stable, secure, and high-performing across different setups.
They also offer staff augmentation and help modernize legacy systems, so you get experienced developers and QA pros right when you need them. The mix of development, testing, and deployment expertise means they can support growth without introducing chaos, while making sure software stays secure and easy to maintain.
Key Highlights:
- Full-cycle development and testing services
- Support for modernizing legacy systems
- Flexible staff augmentation
- Integration of cloud technologies
- Focus on secure and maintainable software
Services:
- API development and testing
- Web and mobile application development
- Cloud development and migration
- Software modernization and customization
- Manual and automated QA testing
- Performance and security testing
- Database development and integration
Contact Information:
- Website: belitsoft.com
- E-mail: info@belitsoft.com
- Facebook: www.facebook.com/Belitsoft
- Twitter: x.com/BelitsoftCom
- LinkedIn: www.linkedin.com/company/belitsoft-llc
- Phone: +44 (20) 3318-18-53
10. Luxe Quality
Luxe Quality focuses on API testing to make sure your software works reliably and securely. They handle both manual and automated testing and cover everything from data checks to access control. One cool thing is that testing can start even before the interface is ready, catching backend issues early and saving time down the road.
They work across different devices, operating systems, and browsers, so your APIs behave consistently. Using tools like Postman, JMeter, and Burp Suite, they help teams spot problems before users ever see them. Their services are flexible, letting you test complex APIs with lots of endpoints while keeping everything in sync with your CI/CD pipelines.
Key Highlights:
- Manual and automated API testing
- Testing across multiple platforms and environments
- Focus on security and data protection
- Early detection of backend issues
- Integration with development workflows
Services:
- API performance testing
- API security testing
- API integration testing
- API automation testing
- Manual API testing
- QA consulting and support
- CI/CD integration for ongoing testing
Contact Information:
- Website: luxequality.com
- E-mail: info@luxequality.com
- Facebook: www.facebook.com/people/Luxe-Quality/100093211400603
- LinkedIn: www.linkedin.com/company/luxequality
- Instagram: www.instagram.com/luxequality_
11. Testrig Technologies
Testrig Technologies focuses on making sure APIs play nicely in bigger software ecosystems. They cover both automated and manual testing, looking at functionality, load, and security across web, mobile, and cloud apps. By working directly within agile workflows, they help development and QA teams stay in sync and catch issues early.
They’re flexible with tools and platforms – think Playwright, Cypress, JMeter, Selenium, Appium, and more. The goal is consistent API behavior, minimized disruptions, and smoother project delivery.
Key Highlights:
- Early defect identification in development
- Support for multiple platforms and technologies
- Integration with agile workflows
- Automated and manual API testing
- Focus on security, performance, and functionality
Services:
- Functional API testing
- Web API testing
- API load testing
- API automation testing
- Security testing
- Agile and continuous testing support
Contact Information:
- Website: www.testrigtechnologies.com
- E-mail: info@testrigtechnologies.com
- Facebook: www.facebook.com/testrig
- Twitter: x.com/testrig_qa
- LinkedIn: www.linkedin.com/company/testrig-technologies
- Address: 2 Myddleton Close, Stanmore HA74WL, London
- Phone: +44 7858506971
12. Daffodil Software
At Daffodil Software, we take a practical approach to API testing as part of our wider software testing services. We mix both manual and automated testing to make sure APIs behave the way they should, handle requests properly, and play nicely with other systems. Our focus is on performance, reliability, and security, helping teams catch problems early and keep API behavior consistent throughout the software’s life. Plus, we look for ways to streamline workflows so releases happen faster and with fewer hiccups.
We use a mix of tools and techniques – everything from dedicated API testing tools to automation frameworks – to cover web and mobile platforms. Our work spans functional checks, performance monitoring, and usability reviews. And we’re not afraid to leverage emerging tech like AI and IoT to predict issues and make testing more efficient. Depending on what you need, we can provide dedicated teams or just augment your existing squad to get the job done.
Key Highlights:
- Supports both manual and automated API testing
- Focus on early defect detection and reliability
- Integration with agile workflows and DevTestOps practices
- Utilizes AI/ML for predictive test analysis
- Flexible engagement models with dedicated or augmented teams
Services:
- API testing services
- Software test automation
- Manual testing for web and mobile applications
- Performance testing and monitoring
- Usability testing
- QA outsourcing and managed QA services
- Test advisory and transformation
Contact Information:
- Website: www.daffodilsw.com
- E-mail: info@daffodilsw.com
- Facebook: www.facebook.com/daffodilsw
- Twitter: x.com/daffodilsw
- LinkedIn: www.linkedin.com/company/daffodil-software-ltd-
- Address: 124 City Road, EC1V 2NX, London, UK
- Phone: +1 518 676 2958
Висновок
When it comes to API testing, having reliable processes in place can make a big difference in how smoothly software runs and integrates with other systems. The companies we’ve looked at approach testing in slightly different ways, but they all focus on making sure APIs behave as expected, handle data correctly, and support secure and stable operations. By combining automated tools with manual checks, they help teams catch problems early and maintain steady workflows.
Choosing the right partner often comes down to the kind of support and expertise your project needs. Some teams bring specialized automation skills, while others provide broader testing services across platforms and devices. Either way, careful API testing can save time, reduce headaches during development, and make sure your software performs reliably in real-world conditions. In the end, it’s about having the confidence that the connections powering your applications won’t let you down.
