We test the APIs your product depends on
Our QA engineers test your REST and GraphQL endpoints by hand and in automated suites. We check that they return the right responses, hold up under load, and handle bad requests the way they should. Every bug we find comes back logged with the request, the response, and the steps to reproduce it.
One endpoint, every part we test
Here's a register call the way you'd see it in a client like Postman. Each part of the request and the response is something we check, so we've labeled them.
The verb, the route, and any query parameters. We test each with valid, missing, and malformed values.
Content-Type and the auth token. The wrong content type or a missing token has to be rejected.
{ "email": "ada@example.com", "password": "S3cur3P@ss!", "name": "Ada Lovelace" }
The fields you send. We push required fields, wrong types, and out-of-range values to see what gets rejected.
201 on success. We confirm the right code on every path, and that a failure never comes back as 200.
{ "id": "usr_8x2k9f", "email": "ada@example.com", "name": "Ada Lovelace", "createdAt": "2026-07-06T10:24:00Z" }
The returned object. We check the schema and the values, and that no password or hash ever comes back.
Practice testing this exact endpoint
The register endpoint above is live on our practice site. Write your own tests against it, no signup and no setup.
How we test every endpoint
Functional testing isn't a single check. For every endpoint we work through each of these areas in turn, from the happy path to the ways it can break. Here's what each one means.
Methods
Which HTTP methods the endpoint allows and that unsupported ones are rejected: GET, POST, PUT, PATCH, DELETE, HEAD, OPTIONS.
Request Headers
Content-Type, Accept, Authorization, and any custom headers, and how the endpoint handles wrong or missing values.
Request Body
Required fields, types, formats, and boundaries, plus malformed payloads, missing fields, unexpected extra fields, and the body content type.
URL and Filters
Path and query parameters, filtering, sorting, pagination, and search, plus how invalid, unknown, or out-of-range values are handled.
Response Headers
Content-Type, caching, CORS, and rate-limit headers, and that each is set the way the contract says.
Response Body
Validated against its schema: fields, types, nullability, and the actual values, not just the shape.
Status Codes
The correct code for each case across 2xx, 3xx, 4xx, and 5xx, checked with and without mocked dependencies and under slow or unreliable connections.
Timings
How long each call takes and whether it stays within the expected response time.
Payload Size
The size of the response body, and that it stays within reasonable, bounded limits.
Authentication
Valid, missing, malformed, and expired tokens each behave correctly. No endpoint answers without proving who is asking.
Authorization (BOLA / BFLA)
One user can't read or change another user's objects, and no role reaches a function it shouldn't. We test object- and function-level access directly.
Business Logic
The rules behind the endpoint hold up: state transitions, calculations, and the constraints a schema check alone would miss.
Idempotency & Side Effects
Retries and duplicate requests don't create duplicate records or double-charge. Writes do exactly what they claim, once.
Data Persistence
What the API says it saved is actually saved, and a later read returns the same thing across the systems behind it.
This is the functional layer. We also cover security and performance, and where it helps we get involved while the contract is still being designed. Tell us about your API and we'll map coverage to your endpoints.
What you get
Testing is the work. These are the things that are yours to keep once it's done.
Postman collections, ready to run
Your endpoints as Postman collections enriched with assertions, or split into a separate collection per endpoint. Structured and documented so your team can run them by hand and keep extending them.
Cypress scripts for E2E coverage
Test scripts written in Cypress that push your coverage beyond single calls into real end-to-end flows, exercising the API the way your app actually uses it.
CI/CD integration for daily regression
Everything wired into your CI/CD pipeline so a full regression run executes on a daily schedule and on every build, catching breakages before they reach production.
How We Work With You
Pick the engagement that fits where you are: a one-off pass before a launch, a fixed-scope test cycle, or an engineer embedded in your team.
Embedded API QA
A dedicated engineer joins your sprints and tests every new endpoint and contract change as it ships, so testing keeps pace with development.
Project Test Cycle
A fixed block of testing against your API. We write the test plan, cover the functional, security, and performance cases, and hand back a full defect report.
Pre-Launch API Check
A quick pass before you ship: we check your critical endpoints, auth, and error handling, and give you a clear go/no-go call when the deadline is tight.
It works. Next we check it holds up under load.
Functional testing confirms each endpoint behaves. But behaving under one request isn't the same as behaving under ten thousand at once. When you need to know where your API slows down or starts dropping requests, our performance testing puts real load on it and finds the limits before your users do.
Ready to Test Your APIs?
Tell us about your API and we'll send back a testing plan. Most teams have our engineers testing real endpoints within a few days.
Frequently Asked Questions
Common questions about our API testing services.
What should I look for in an API testing company?
Look for an API testing company that covers functional, integration, performance, and security testing, automates against your CI/CD pipeline, and delivers clear documentation. AssertQA does this with Postman and Cypress so your APIs stay reliable as they change.
Do you offer end-to-end and automated API testing services?
Yes. We provide end-to-end API testing services including automated REST API test suites that run in your pipeline, catching breaking changes early and reducing manual effort on every release.
Which tools do you use for REST API testing?
We use Postman to build and run API tests, Cypress to extend coverage into end-to-end flows, and wire everything into your CI/CD pipeline, chosen to fit your stack so the tests stay easy for your team to maintain.
Can you integrate API tests into our CI/CD pipeline?
Absolutely. We integrate automated API tests directly into your CI/CD pipeline and can set up monitoring, so every build validates your endpoints and you catch regressions before they reach production.
Do you test API security and performance?
Yes. Beyond functional checks, we validate API security and performance, testing authentication, error handling, and behavior under load so your APIs stay safe and responsive at scale.
Do you use AI in your API testing work?
Yes, we use AI where it genuinely helps, for example to speed up test case generation. But AI doesn't do the work for us. Every test suite is designed and reviewed by our QA engineers.
What Our Clients Say...
Don't just take our word for it - hear from the teams we've helped succeed
We've been partnering with AssertQA since 2023, and the impact on our product quality has been substantial. Their QA team has become an integral part of our development process, catching issues early and helping us maintain the reliability our clients expect from a financial services platform.
We've been relying on AssertQA's manual testing services at dizmo AG for over five years—initially for our desktop product, and later for our SaaS resource planning platform, Planisy. AssertQA has proven to be a dependable and proactive partner, consistently going the extra mile.
We were rolling out our solution for a client and brought in AssertQA to help with test automation. From day one, they were hands-on, professional, and really cared about making sure everything worked perfectly.
AssertQA has provided us with a range of services across multiple projects we've worked on together. Their automation capabilities are outstanding and integrate quickly into the development team, improving the team's overall efficiency and making the product more robust.
I had the pleasure of collaborating with the AssertQA team on the Efinity project. What sets Tatjana and her team apart is their combination of expertise, dedication, and a professional approach to every task.
AssertQA has been a great partner throughout our mobile automation journey. They helped us navigate the initial challenges, provided practical solutions when we were blocked, and played an important role in getting us started successfully.
