20 Best API Testing Companies (2026)
Modern software rarely operates as a single standalone product anymore. Applications exchange data with payment gateways, cloud platforms, mobile apps, customer portals, and countless third-party services. When those connections fail, the problem is often invisible until users begin encountering errors. That is why API testing has become a critical part of software quality assurance, helping businesses identify issues before they affect production systems.
This list highlights API testing companies that specialize in validating integrations, automating test workflows, and ensuring that APIs perform reliably under real-world conditions. Some focus exclusively on quality assurance, while others provide API testing as part of broader software engineering services. Each company brings a different mix of technical expertise, testing methodologies, and industry experience, giving organizations a range of options depending on the complexity of their systems and development goals.
1. Oski Solutions
At Oski Solutions, we work with companies that rely on multiple applications, platforms, and data sources to keep daily operations running smoothly. API testing is an important part of that process. We help businesses verify that APIs exchange data correctly, remain stable during updates, and continue working as expected when connected systems evolve. Our projects often involve custom software environments where APIs connect e-commerce platforms, payment gateways, ERP systems, CRM tools, and internal business applications.
Much of our work takes place in organizations that are modernizing older systems or scaling their digital infrastructure. In these situations, API testing is rarely an isolated task. It sits alongside software development, cloud implementation, integrations, and ongoing system maintenance. We use our experience with technologies such as .NET, Node.js, PHP, C#, Azure, AWS, and various database platforms to validate integrations across complex environments.
Key Highlights:
API testing for custom software ecosystems
Experience with third-party and custom API integrations
Support for legacy system modernization projects
Work with cloud-based and hybrid environments
Agile and remote-friendly delivery approach
Experience across e-commerce, fintech, healthcare, and logistics
Services:
API testing
API integration validation
Custom API development
CRM and ERP integrations
Payment gateway integrations
Software integration testing
Cloud solutions development
Custom software development
Contact Information:
Website: oski.site
E-mail: [email protected]
LinkedIn: www.linkedin.com/company/oski-solutions
Address: Kaupmehe tn 7, 10114 Tallinn, Estonia
Phone: +48571282759
API Testing Services
Test APIs for functionality, performance, security, and reliability to ensure seamless integrations with an experienced testing team.
2. Testriq
Testriq focuses heavily on API quality assurance, with testing services built around REST, GraphQL, SOAP, and other modern API architectures. Their team approaches API testing as a core part of software reliability rather than a final verification step. Alongside functional validation, they examine performance, security, and how APIs behave within larger distributed systems. The company also follows the ISO 29119 testing framework, which shapes its approach to planning, execution, and documentation.
A noticeable part of Testriq's work is the emphasis on automated testing and continuous integration workflows. They support organizations that need API validation integrated into CI/CD pipelines and use a range of testing frameworks and security tools to support that process. Beyond endpoint testing, Testriq also addresses schema stability, runtime behavior, compliance requirements, and API-level security controls.
Key Highlights:
Focus on REST, GraphQL, SOAP, and gRPC testing
API testing aligned with ISO 29119 standards
Automated testing integrated into CI/CD workflows
Security and compliance-oriented testing approach
Services:
API testing
REST API testing
GraphQL testing
SOAP API testing
API performance testing
API load testing
API security testing
Contact Information:
Website: www.testriq.com
E-mail: [email protected]
Facebook: www.facebook.com/testriq.lab
Twitter: x.com/testriq
LinkedIn: www.linkedin.com/company/testriq-qa-lab
Instagram: www.instagram.com/testriq
Address: Office #2, 2nd Floor, Ashley Tower, Kanakia Road, Vagad Nagar, Beverly Park, Mira Road, Mira Bhayandar, Mumbai, Maharashtra 401107
Phone: (+91) 915-2929-343
3. A-listware
A-listware provides API testing as part of a broader software engineering and consulting offering. Their API testing services focus on verifying application reliability and helping systems communicate consistently across cloud-based and on-premises infrastructures.
Rather than operating solely as a testing provider, A-listware combines API validation with development support, dedicated teams, and consulting services. They work with businesses in sectors such as healthcare, finance, retail, transportation, and telecommunications, where software integrations often play a central role in daily operations.
Key Highlights:
API testing integrated with software development services
Support for cloud and on-premises environments
Team augmentation and outsourcing options
Experience across multiple regulated industries
Flexible collaboration models
Infrastructure and cybersecurity expertise
Services:
API testing
Quality assurance
Software development
Application services
UX/UI design
IT consulting
Dedicated development teams
Contact Information:
Website: a-listware.com
E-mail: [email protected]
Facebook: www.facebook.com/alistware
LinkedIn: www.linkedin.com/company/a-listware
Address: St. Leonards-On-Sea, TN37 7TA, UK
Phone: +44 (0)142 439 01 40
4. Belitsoft
Belitsoft approaches API testing as an ongoing activity that runs alongside software development rather than after it. Their engineers work with APIs throughout the development lifecycle, helping identify functionality, security, performance, and integration issues before they affect larger systems. The company combines automated and manual testing methods and integrates testing activities into CI/CD environments to support continuous delivery processes.
What sets Belitsoft apart is the breadth of API testing areas they cover. Their work includes performance evaluation, reliability checks, security assessments, negative testing, integration validation, regression testing, and runtime error detection.
Key Highlights:
API testing integrated into development workflows
Automated and manual testing methodologies
Focus on performance, reliability, and security
CI/CD integration support
Testing for public, private, and partner APIs
Services:
API functional testing
API performance testing
API security testing
API load testing
API reliability testing
API regression testing
API integration testing
Contact Information:
Website: belitsoft.com
E-mail: [email protected]
Facebook: www.facebook.com/Belitsoft
Twitter: x.com/BelitsoftCom
LinkedIn: www.linkedin.com/company/belitsoft-llc
Address: 26/28 Hammersmith Grove, London W6 7HA
Phone: +44 (20) 3318-18-53
5. DeviQA
DeviQA is a quality assurance company that provides API testing alongside a wider range of testing and quality engineering services. Their API testing offering covers functional validation, performance checks, security reviews, regression testing, and integration testing. They work with both startups and larger organizations, supporting products across sectors such as healthcare, fintech, logistics, retail, and manufacturing.
A notable aspect of DeviQA's approach is the combination of traditional QA processes with automation and AI-assisted testing tools. The company also offers several engagement models, including dedicated QA teams, staff augmentation, managed QA services, and project-based outsourcing. API testing is integrated into broader quality assurance workflows that include web, mobile, SaaS, and enterprise applications.
Key Highlights:
API testing as part of a broader quality engineering practice
Coverage of functional, security, performance, and regression testing
AI-assisted testing workflows
Dedicated QA teams and managed QA services
Experience across healthcare, fintech, logistics, and retail
Services:
Test automation
API performance testing
Mobile application testing
API security testing
API test automation
Web application testing
API integration testing
API regression testing
Contact Information:
Website: www.deviqa.com
E-mail: [email protected]
Facebook: www.facebook.com/deviQASolutions
LinkedIn: www.linkedin.com/company/deviqa
Address: 9 Brighton Terrace, London
Phone: +1 805 491 9331
6. Qualitest
Qualitest provides API testing services within a larger quality engineering and digital transformation practice. Their work focuses on validating APIs while taking into account both technical requirements and broader business objectives. They evaluate how APIs support larger systems, integrations, and business processes.
The company has experience with public, private, and partner APIs, as well as REST and SOAP architectures. Automation plays a significant role in their testing approach, supported by custom frameworks, service virtualization, and performance testing capabilities.
Key Highlights:
API testing aligned with business and technical requirements
Experience with REST and SOAP environments
Service virtualization capabilities
Automated testing frameworks
Support for Agile and DevOps workflows
Services:
API automation
API performance testing
Contract testing
API testing
Service virtualization
Cloud assurance
Test automation
Contact Information:
Website: www.qualitestgroup.com
Facebook: www.facebook.com/Qualitestgroup
Twitter: x.com/QualiTest
LinkedIn: www.linkedin.com/company/qualitest
Instagram: www.instagram.com/lifeatqualitest
Address: Paraguay 577 – Piso 9 Oficina B, Buenos Aires, C1057AAE, Argentina
Phone: (312) 763-6693
7. QAwerk
QAwerk specializes in software testing and quality assurance, with API testing forming part of its broader testing expertise. API testing is treated as a technical discipline that requires a detailed understanding of how applications communicate behind the user interface.
Alongside manual testing activities, QAwerk also provides API automation services using tools such as Postman, Swagger, SoapUI, JMeter, and Katalon Studio. The company works with web, mobile, desktop, and other software products, and it also offers technical writing services related to API documentation. Their testing process includes specification reviews, test design, execution, reporting, and framework development.
Key Highlights:
Focus on API functionality, security, and reliability
Automated and manual API testing services
API documentation support
Test framework development
Experience with web, mobile, and desktop applications
Structured testing process from review to reporting
Services:
API testing
API performance testing
Test case development
API security testing
API automation testing
Test execution and reporting
API integration testing
API specification review
Contact Information:
Website: qawerk.com
E-mail: [email protected]
Facebook: www.facebook.com/QAwerk
Twitter: x.com/qawerk
LinkedIn: www.linkedin.com/company/qawerk
Instagram: www.instagram.com/qawerk.testing
Address: Ivana Franka St 20b, 01030, Ukraine, Kyiv
Phone: +372 5368 6363
8. Net Devs
Net Devs develops enterprise software and cloud-based systems, with testing built into the delivery process from the earliest stages through deployment. Since they work across .NET, JVM, Node.js, Python, and Go environments, API validation is closely connected to backend development, integrations, and platform engineering activities.
The company follows a senior-led delivery model where architecture decisions, quality reviews, and technical oversight remain in the hands of experienced engineers. Net Devs also incorporates AI-assisted workflows into development and testing processes while keeping final verification and quality control under human supervision. Their API testing work supports cloud-native systems running on Azure, AWS, and GCP.
Key Highlights:
API testing integrated into software delivery workflows
Senior engineer oversight throughout development
Automated and manual QA practices
Experience with cloud-native environments
Services:
Quality assurance
Enterprise software development
Cloud and platform engineering
API testing
Frontend development
Automated testing
Contact Information:
Website: net-devs.com
E-mail: [email protected]
LinkedIn: www.linkedin.com/company/net-devs
Address: Obrzeżna 1D, 02-691 Warszawa, Poland
Phone: +48 571 282 759
9. TestingXperts
TestingXperts provides API testing services as part of its broader software testing and quality assurance practice. Their work covers the full API lifecycle, from validating individual endpoints to checking how APIs interact with applications and connected systems. The company serves organizations across industries including healthcare, telecommunications, banking, retail, and e-commerce.
Their API testing offering includes functional validation, load testing, security assessments, runtime error detection, and contract testing. TestingXperts also examines interactions between clients, servers, and APIs to verify that data exchanges occur as expected.
Key Highlights:
End-to-end API testing services
Coverage of functional and load testing
Contract testing capabilities
Runtime error detection
Security-focused validation
Services:
Unit testing
API testing
Functional testing
Load testing
Security testing
Contract testing
Runtime error detection
Contact Information:
Website: www.testingxperts.com
E-mail: [email protected]
Facebook: www.facebook.com/testingxperts
Twitter: x.com/TestingXperts
LinkedIn: www.linkedin.com/company/testingxperts
Address: 2425 Matheson Boulevard East, 8th Floor, Mississauga Ontario, L4W 5K4
Phone: +1 437 577 2725
10. KiwiQA
KiwiQA focuses on software testing and digital assurance services, with API testing forming one part of its testing portfolio. Their approach centers on verifying functionality, reliability, security, and performance before APIs are released into production environments. The company uses both manual and automated testing methods and places emphasis on structured test planning and organized test execution.
Along with standard functionality checks, KiwiQA conducts reliability, load, security, and negative testing to evaluate how APIs behave under different conditions. Their testing process also includes prioritizing API functions, grouping test cases by category, and automating repetitive testing activities where appropriate. API testing is supported by a broader range of QA services that cover automation, performance, mobile, and security testing.
Key Highlights:
Structured API testing methodology
Automated and manual testing approaches
Focus on functionality, reliability, and security
Negative testing capabilities
Integration with broader QA services
Experience with automation-focused testing workflows
Services:
Automated API testing
API functionality testing
API reliability testing
API load testing
API security testing
Negative testing
Automation testing
Performance testing
Contact Information:
Website: www.kiwiqa.com
E-mail: [email protected]
Facebook: www.facebook.com/kiwiqaservicesptyltd
Twitter: x.com/KQSPL
LinkedIn: www.linkedin.com/company/kiwiqa-services
Instagram: www.instagram.com/kiwiqa_services
Address: Suite 309, 20A Lexington Drive, BellaVista, NSW 2146
Phone: +61 472 869 800
11. Lengreo
Lengreo combines API testing with a broader focus on business growth services. Alongside validating API functionality, performance, and security, they also work in areas such as lead generation, digital marketing, and sales development. Their testing activities are aimed at helping organizations maintain stable data exchange between systems while supporting the technical side of product growth.
Beyond API-related work, Lengreo develops outreach and marketing programs that include email campaigns, LinkedIn engagement, SEO, content creation, and paid advertising. The company works at the intersection of technical validation and customer acquisition, bringing together software-focused and marketing-focused services under one structure.
Key Highlights:
API functionality, performance, and security testing
B2B lead generation services
Sales funnel analysis and optimization
Email and LinkedIn outreach campaigns
SEO and content marketing support
Services:
API testing
Performance testing
Security testing
Lead generation
Appointment setting
Digital marketing strategy
Content marketing
Contact Information:
Website: lengreo.com
E-mail: [email protected]
Twitter: x.com/Lengreo
LinkedIn: www.linkedin.com/company/lengreo
Instagram: www.instagram.com/lengreo.agency
Address: Vrijstraat 9 C/D, 5611 AT Eindhoven, Netherlands
Phone: +31 686 147 566
12. AssertQA
AssertQA provides software quality assurance services with API testing as one of its core testing areas. Their team works with REST and GraphQL APIs, focusing on functionality, performance, security, and integration behavior throughout the API lifecycle. Testing activities are supported by tools such as Postman, REST Assured, and Newman, which are also used for automation and CI/CD integration.
Documentation and long-term test maintenance are included in their approach, allowing teams to continue using testing assets after implementation. AssertQA also supports automated monitoring within development pipelines, helping organizations identify API issues before they affect other parts of the software environment.
Key Highlights:
Testing for REST and GraphQL APIs
Functional, security, and performance validation
CI/CD integration support
Automated API test implementation
Services:
Functional testing
Performance testing
Security testing
Integration testing
Automated testing
CI/CD test integration
API testing
API documentation
Contact Information:
Website: assertqa.com
Twitter: x.com/assertqa
LinkedIn: www.linkedin.com/company/assertqa
Instagram: www.instagram.com/assertqa
13. White Test Lab
White Test Lab focuses on software testing and quality assurance, with API testing offered as part of a broader testing portfolio. Their process begins with reviewing requirements and API documentation before selecting testing methods, environments, and tools that fit the software being evaluated.
API testing at White Test Lab covers functionality, reliability, integrations, regression testing, end-to-end validation, and both manual and automated execution. They also provide ongoing test maintenance for teams that continue releasing updates and new features after the initial testing phase.
Key Highlights:
Combination of manual and automated API testing
Multiple testing methodologies used during execution
API documentation review and analysis
Support for ongoing test maintenance
End-to-end and integration testing capabilities
Services:
API testing
Automated API testing
Manual API testing
API functional testing
API reliability testing
API integration testing
API regression testing
End-to-end API testing
Contact Information:
Website: white-test.com
E-mail: [email protected]
LinkedIn: www.linkedin.com/company/white-test-lab
Phone: +380 66 364 13 53
14. Gilzor
Gilzor approaches API work as part of a broader software architecture process, focusing on how applications, services, and systems exchange information. Their team works with backend interfaces that connect web platforms, mobile applications, and third-party tools, paying attention to endpoint structure, authentication, access management, and data consistency.
As products evolve, Gilzor also works on extending and refining existing APIs. That can involve improving maintainability, addressing performance concerns, simplifying complex integrations, or adjusting data flows as business requirements change. API testing supports these efforts by helping verify that interfaces continue to function correctly as systems grow and become more interconnected.
Key Highlights:
API-focused backend architecture support
Third-party integration expertise
Attention to authentication and access control
Support for both new and existing API environments
Focus on maintainability and long-term system stability
Services:
API development
API testing
Third-party integrations
Web application development
Mobile application development
Business analysis
Quality assurance
System planning
Contact Information:
Website: www.gilzor.com
E-mail: [email protected]
LinkedIn: www.linkedin.com/company/gilzor-softwaredevelopment
Address: Poland, Warsaw, Office 58, street Adama Mickiewicza 37, 01-625
15. SoftPro
SoftPro develops custom software solutions for businesses that need modern web applications, cloud systems, and digital tools. Their technology stack includes Azure, ASP.NET, .NET Core, and other Microsoft technologies, which are often used in systems where APIs play an important role in connecting applications, services, and data sources. API testing helps ensure that these connections remain reliable and support smooth communication across different software components.
SoftPro also combines software engineering with cloud development and artificial intelligence services, making API quality an important consideration when integrating different technologies into a single solution.
Key Highlights:
Experience with Microsoft-based technologies
Cloud and web application development services
API validation within custom software environments
Frontend and backend development capabilities
Services:
API testing
Software development
Web application development
Cloud development
Artificial intelligence solutions
Backend development
Frontend development
Contact Information:
Website: soft-pro.pl
LinkedIn: www.linkedin.com/in/kyrylo-o
Address: Mazowieckie Voivodeship, 13 Erasmus Ciołka St. 401, Warsaw, Poland
Phone: +48 571 282 759
16. SaM Solutions
SaM Solutions provides API testing services as part of a larger quality assurance practice covering web, mobile, desktop, hybrid, and IoT software. Their testing activities focus on both functional and non-functional aspects of APIs, including request handling, response validation, performance behavior, and security requirements.
Operating as an international QA provider, SaM Solutions supports organizations that need API testing integrated into broader software testing processes. Their team works with tools such as Postman, SoapUI, and RestAssured while also offering related services in performance testing, security testing, accessibility, compatibility, and platform-specific validation.
Key Highlights:
API testing for web, mobile, desktop, and IoT software
Functional and non-functional testing coverage
Manual and automated testing approaches
Security and performance validation
Support for platform-specific testing needs
Services:
Functional API testing
Performance testing
API testing
Security testing
Automated testing
Integration testing
Mobile application testing
Contact Information:
Website: sam-solutions.com
E-mail: [email protected]
Facebook: www.facebook.com/SaMSolutionsCOM
Twitter: x.com/SaMSolutionsCom
LinkedIn: www.linkedin.com/company/sam-solutions
Address: Roemerstrasse 32, 82205 Gilching, Germany
Phone: +49-8105-399-050
17. Mobian
Mobian develops mobile applications, custom software, and AI-powered solutions for organizations in healthcare, fintech, logistics, and technology-related sectors. Since many of these systems depend on communication between multiple services, API testing plays an important role in validating integrations, data exchange, and application stability. Their teams work with both newly developed products and existing software environments where APIs connect mobile apps, backend systems, cloud services, and third-party platforms.
The company operates through both outsourcing and team augmentation models, supporting clients that need either full product delivery or additional engineering capacity.
Key Highlights:
Experience with healthcare, fintech, and logistics software
API validation for mobile and backend ecosystems
Clinical Trial Management System expertise
Support for legacy system integrations
Dedicated teams and team augmentation options
Focus on secure data exchange
Services:
API testing
Mobile application development
Custom software development
Clinical trial management systems
Healthcare software development
AI solutions development
Contact Information:
Website: mobian.studio
Email: [email protected]
LinkedIn: www.linkedin.com/company/mobian-studio
Address: Harju maakond, Tallinn, Kesklinna Linnaosa, Masina tn 22, 10113
18. Codemech Solutions
Codemech Solutions provides API testing services alongside software, web, cloud, and mobile development. Their testing work focuses on evaluating API functionality, security, reliability, integration behavior, and performance across different architectures and communication formats. The company supports APIs built with REST, SOAP, GraphQL, JSON, XML, and related technologies.
Codemech Solutions also works across industries such as healthcare, travel, education, logistics, retail, construction, and e-commerce, where software systems often depend on communication between multiple services and platforms. Testing activities are combined with automation, regression testing, load testing, and CI/CD support to help maintain API quality throughout development cycles.
Key Highlights:
Support for REST, SOAP, and GraphQL APIs
Automated API testing capabilities
Performance and load testing services
CI/CD pipeline support
Third-party integration validation
Services:
Functional testing
Integration testing
Security testing
API testing
Performance testing
Load testing
Contact Information:
Website: www.codemechsolutions.com
E-mail: [email protected]
Facebook: www.facebook.com/codemechsolutions
Twitter: x.com/codemech_sol
LinkedIn: www.linkedin.com/company/codemechsolutions
Instagram: www.instagram.com/codemechsolution
Address: 402, Swasthi Business Center, SP Ring Rd. Nikol Ahmedabad GJ 382350, India
Phone: +91 798 494-9224
19. 21Century.Tech
21Century.Tech is an AI-focused software studio that combines senior engineering oversight with AI-assisted development workflows. Their delivery process includes software architecture, code review, testing, documentation, and deployment, with API testing forming part of the quality assurance activities that support production-ready releases.
21Century.Tech integrates testing into its broader engineering workflow. Automated test generation, documentation, refactoring, and integration work are supported by AI tools, while architectural decisions, security reviews, and final quality checks remain under direct human responsibility.
Key Highlights:
AI-assisted software development workflows
Senior engineer review of all delivered code
Support for third-party integrations
Integrated testing and documentation processes
Focus on production-ready software delivery
Services:
Software development
Third-party integrations
MVP development
API testing
Legacy system refactoring
Test automation
Contact Information:
Website: 21century.tech
E-mail: [email protected]
20. Crestech Software
Crestech Software provides API testing as part of its broader functional quality assurance services. Their team focuses on validating API functionality, security, reliability, and performance while adapting testing strategies to the specific business rules and requirements behind each application.
Crestech Software supports automation, load testing, integration testing, and negative testing to help identify issues before they affect connected systems. Their API testing services are used across web, mobile, IoT, enterprise, and legacy environments, where stable communication between software components is essential for day-to-day operations.
Key Highlights:
API testing aligned with business requirements
Functional and non-functional testing coverage
Support for web, mobile, IoT, and legacy platforms
Automated API testing capabilities
Services:
API testing
API functional testing
Manual functional testing
Performance testing
API automation testing
Negative testing
API security testing
API integration testing
Contact Information:
Website: www.crestechsoftware.com
E-mail: [email protected]
Facebook: www.facebook.com/crestechsoftware
Twitter: x.com/crestech
LinkedIn: www.linkedin.com/company/crestech-software-systems
Instagram: www.instagram.com/crestech_software
Address: 1781, 19th Main Rd, Vanganahalli, 1st Sector, ground floor HSR Layout, Bengaluru, Karnataka 560102
Phone: +91-8826666755
Conclusion
Choosing an API testing company is rarely about finding the biggest name on the list. What usually matters more is whether the team understands how APIs fit into the larger software ecosystem and whether they can spot issues before those issues reach production. As applications become more connected through integrations, cloud services, and microservices, reliable API testing has become a core part of software quality rather than a separate technical task.
The companies featured in this article approach API testing from different angles. Some focus heavily on automation and CI/CD integration, while others place more emphasis on security, performance, or long-term QA support. The right choice depends on the complexity of your systems, your release cycle, and the level of testing expertise already available inside your organization. Taking time to compare capabilities, communication style, and testing coverage can make a noticeable difference in the stability and reliability of the software you deliver.
