Payments, account data, partner integrations, web apps, and mobile apps all depend on APIs that change often and fail quietly. A wrong field, a missing authorization check, or a timeout under load can reach production without breaking a single screen of the user interface.
Our API testing solutions help teams build reliable digital products and release API changes with confidence. We combine automated API testing with expert human review to validate the functionality, reliability, performance, and security of REST and SOAP APIs and the integrations between your systems.
Releasing API changes every sprint?
Most API failures surface far from where they started. These are the six risks we help you control:
API testing reduces production failures by finding these issues early in the development process, when they are faster and cheaper to fix.
AI speeds up the repetitive parts of API testing. It can generate test cases from API documentation and specifications, build test data, keep test suites up to date as contracts change, and help analyze failures. That reduces manual testing of repetitive checks when testing APIs at scale.
Our engineers focus on what automation cannot judge alone. They model the core business logic, design negative and abuse scenarios with invalid inputs, and decide where testing effort brings the most risk reduction.
We cover seven areas of API quality, from the business logic in each response to how the API behaves in production.
Functional API testing checks the API's functionality against its specifications and API requirements: values, states, calculations, the status code of each response, error messages, and error handling. It confirms that business rules are applied and that data integrity holds before data reaches the frontend.
Contract testing keeps service consumers and producers aligned and helps prevent breaking updates. Schema validation and contract tests in your CI/CD pipeline detect changes between providers and consumers before they reach a shared testing environment.
Automated regression testing catches regressions early and checks that updates do not break existing functionality. Our test automation team builds fast, reliable automated testing suites that run automatically on every code change and cover the API endpoints that matter most to your business.
API performance testing evaluates speed, scalability, and reliability under load and helps identify response-time issues and bottlenecks. Load testing measures how the API performs under expected traffic, and stress testing pushes it beyond normal capacity to see how it recovers.
API security testing includes penetration testing and the evaluation of access controls, authentication, input validation, rate limits, encryption, and data exposure, prioritized with the OWASP API Security Top 10. It helps uncover vulnerabilities and security risks before attackers can exploit them.
Integration testing verifies that APIs communicate correctly with other services. When third parties or internal systems are unavailable or costly to call, we test system integration with service virtualization and mocks.
Detect issues before customers report them by connecting tests with API monitoring and observability.
Our approach is grounded in Quality Intelligence: combining technical context, business rules, and expert knowledge to make better release decisions.
For APIs, that means connecting specifications, test results, and production signals so teams know which changes are safe to release. AI agents built on Tero, our open-source agent harness, can analyze API changes, generate tests from specifications, and investigate failures with defined permissions and human checkpoints. Our approach is grounded in Quality Intelligence: using artificial intelligence, engineering context, test evidence, and human expertise to understand system behavior and improve release decisions.
We support API quality from the first assessment to continuous improvement, in six stages, with proven methodologies that adapt to your project demands.
We inventory your APIs, including undocumented and deprecated versions, review current test coverage and risks, and deliver a prioritized roadmap.
We design a testing strategy that combines unit testing, contract testing, integration testing, end-to-end tests, performance testing, and security testing, mapped to business risk and to your development workflow.
Our automation testing team builds and maintains API test automation with testing tools such as Postman, REST Assured, SoapUI, and WireMock, covering REST and SOAP APIs. Postman collections can run with the Postman CLI as quality gates in continuous integration.
We run load, stress, and resilience tests with JMeter, k6, and jmeter-dsl, the open-source tool we created, alongside API security testing.
We prepare realistic test data and anonymize sensitive information so tests reflect production without exposing customers.
We track coverage, failure trends, and flaky tests over time, using production observability data to refine test scenarios and keep test suites aligned with real API usage
In banking, payments, and healthcare, API testing also has to produce evidence. Standards such as PCI DSS, regulations such as the EU's DORA, and the HIPAA Security Rule shape how APIs are tested, documented, and monitored, and they raise the bar for thorough testing of sensitive endpoints. API security testing helps support compliance with those frameworks through deeper authorization and data protection tests, traceability from requirement to result, protected test data, and closer attention to third-party and resilience risks.
Three examples of how we strengthened the quality of APIs that carry money and data:
API testing is the practice of validating application programming interfaces directly, by sending requests and checking that responses return the correct data, without going through a user interface. It checks that APIs function as expected and covers functionality, contracts, error handling, performance, and security. It also validates that APIs communicate correctly with other services.
Comprehensive API testing services evaluate the functionality, reliability, performance, and security of APIs. They usually include an assessment of current APIs and coverage, a test strategy, automated functional and regression tests, contract testing, performance and security testing, test data management, and integration with CI/CD and monitoring.
API test coverage includes validating status codes, response bodies, schemas, and error handling for each endpoint, plus business rules, authorization, and behavior under load.
API testing validates the API layer directly through requests and responses. Functional testing validates that features behave as expected for users, through UI testing or the API, and functional API testing is the part that runs at the API layer. API tests run faster and catch critical bugs earlier, while UI-level functional tests confirm the full user journey.
Automated API testing runs repeated tests without manual intervention, on every code change. API tests execute fast, which fits continuous integration and CI/CD pipelines, and automation broadens test coverage across endpoints, devices, and services.
Technical expertise is key when choosing an API testing company. Whether you are a CTO or a QA manager, look for proven experience in your domain, automation expertise, coverage of both functional and non-functional testing (performance and security), testing tools that fit your stack, and results that engineering, risk, and compliance teams can review. Ask for case studies with measurable outcomes and how people review what AI produces.
APIs in regulated industries are tested with the same testing techniques as any API, plus stricter authorization and data protection tests, traceability from requirements to results, protected test data, documented evidence, and testing of third-party dependencies. The exact scope depends on frameworks such as PCI DSS, DORA, or HIPAA.
Contract testing checks that an API provider and its consumers agree on request and response formats. It detects breaking changes early, before services are deployed together, and reduces the need for slow end-to-end tests.
API security is tested by checking authentication, object-level and function-level authorization, input validation, rate limiting, data exposure, encryption, and configuration. The OWASP API Security Top 10 is a common reference to prioritize those tests, and API security testing services usually add penetration testing.
We work with the tools that fit your stack, including Postman, REST Assured, SoapUI, and WireMock for functional and contract tests, and JMeter, k6, and jmeter-dsl for performance tests. Our article on API testing tools compares common options and their advanced features.
AI helps with API testing by generating test cases from specifications, creating test data, updating tests when contracts change, and analyzing failures. Expert review stays in the loop to validate business rules and prioritize risk.
Deep experience in software testing, combining functional, performance, and security testing across complex systems.
Count on our team for effective API testing that validates functionality, contracts, performance, and security across your APIs, and builds the evidence behind every release. Get in touch with us today!
