API testing services
The interface gets the attention, but the API does the work. The worst bugs I've found never drew a pixel: a 200 response with a failure in the body, a retry that created the same order twice, a timeout in one service that queued up behind three others.
An API can lie with a straight face. I've tested endpoints that returned 200 OK with a failed status tucked inside the response body, and the frontend showed a success screen while the order quietly went nowhere. No crash, no visible error, nothing for a user to report. UI testing alone won't catch this class of bug, because the interface only reports what it was told.
So we test the API as a product in its own right. Every endpoint gets checked for what it returns and for how it fails: wrong status codes, expired tokens, malformed payloads, boundary values, empty lists, page two of a paginated response that nobody ever opened. We explore in Postman and write the repeatable checks as code, so they run in your CI on every merge, in seconds rather than the minutes a browser suite needs.
If you have integrated microservices, this layer matters double. Every service boundary is a contract two teams believe they agree on, and those beliefs drift: one team renames a field, deploys on Tuesday, and a consumer three services away starts failing on Thursday with an error that names neither of them. We write consumer-driven contract tests with Pact so a breaking change fails a build, not production. And we test the ugly distributed cases besides: retries that must be idempotent, timeouts that cascade, and what service B actually does when service A returns garbage.
There's a selfish reason to test here too: it's the cheapest layer that can catch most defects. An API check needs no browser, no rendered page and no flaky selector; it either got the right response or it didn't. Teams that push the bulk of their checks down to this layer get faster pipelines and calmer release days, and keep a thin set of browser tests for the things only a browser can prove.
A concession: API tests can't see your product. They will never notice the invisible checkout button on iOS Safari or the layout that collapses in German. So we don't sell API testing as the whole answer; we pair it with UI checks and exploratory sessions sized to your product. But when a field goes missing from a response at 2am, it's the API suite that catches it. We find it before your users do.
REST & GraphQL endpoint testing
Status codes, response bodies, headers and error shapes checked for every endpoint, including the failure cases happy-path tests skip.
Contract testing for microservices
Consumer-driven contracts with Pact catch a breaking change at build time, before one team's deploy becomes another team's incident.
Negative and edge-case coverage
Expired tokens, malformed payloads, boundary values, rate limits and retry idempotency: the requests real clients actually send.
API checks in your CI pipeline
Fast, browser-free checks wired into your pipeline, so every merge is verified in seconds and results land in the pull request.
Frequently asked questions
We already have end-to-end UI tests. Do we need API testing as well?
Usually, yes. UI tests exercise one rendered path through your product; API tests can cover hundreds of input and failure combinations in the time a browser suite takes to log in. They also fail more precisely: a broken endpoint names itself, rather than surfacing as a timeout two screens later. Keep a lean UI suite for what only a browser can prove and test the rest at the API layer.
What is contract testing, and do we need it?
A contract test records what a consumer actually needs from a provider's API, which fields, which types, which status codes, and verifies the provider still honours it on every build. If you run integrated microservices maintained by more than one team, it is the cheapest protection available against the classic failure: a renamed field deployed by one team breaking a service owned by another. A monolith with one internal API usually doesn't need it yet.
Can you test our microservices without spinning up the whole environment?
Mostly, yes. Contract tests and mocked dependencies let us verify each service in isolation, which is faster and far less brittle than a full staging deployment for every check. The honest caveat: mocks drift from reality, so we also keep a small set of tests that run against genuinely integrated environments. A suite that only ever talks to mocks will happily stay green while the real integration burns.
Which tools do you use for API testing?
Postman for exploratory work and quick reproduction, code-based checks for anything that runs in CI, Pact for consumer-driven contracts, and schema validation against your OpenAPI spec. The tool matters less than the test cases: one well-chosen negative test in a plain HTTP client beats an exhaustive happy-path suite in the fanciest framework.
How do you test the third-party APIs we depend on?
We don't test them; we test you against them. You can't fix Stripe or a courier's tracking API, but you control what your product does when they return a 500, hang for thirty seconds or change a payload without notice. We simulate exactly those failures and check that your system degrades politely: clear user messaging, no double charges, no stuck orders. Most teams discover their retry logic in production; it's cheaper to meet it in a test.
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