Invalid input handling
Send malformed, missing or boundary-value payloads and check the response.
ValidationErrorsPayloads
API Testing
API testing for real backend behaviour
I check how the API behaves with real, invalid and unexpected data — and whether the frontend handles those responses properly.
When this helps
Use this when the product depends on backend states, permissions, validation or integrations. API testing helps find issues that are easy to miss if you only test through the UI.
What I check
- Endpoint request and response checks
- Required fields, empty values and invalid payloads
- Status codes and error message behaviour
- Auth, permissions and role-based access
- Frontend and backend state comparison
- Postman request and collection notes
Common problems
Invalid input returns a server error instead of validation
I check how this behaves in the real flow and whether it can block, confuse or mislead a user.
Required fields are accepted as empty or null
I check how this behaves in the real flow and whether it can block, confuse or mislead a user.
The frontend shows failure while the backend returns success
I check how this behaves in the real flow and whether it can block, confuse or mislead a user.
Different roles get inconsistent API behaviour
I check how this behaves in the real flow and whether it can block, confuse or mislead a user.
Error responses are too vague for the UI to guide the user
I check how this behaves in the real flow and whether it can block, confuse or mislead a user.
Success and failure responses use different structures without clear reason
I check how this behaves in the real flow and whether it can block, confuse or mislead a user.
Example checks
What you get
API issue reports
Requests, responses, expected behaviour, actual behaviour and product impact.
Postman notes
Improved requests, environments, assertions or collection structure where useful.
Backend risk summary
A short overview of inconsistent endpoints, weak validation and retest priorities.
Example finding
Endpoint: POST /api/v1/orders Scenario: Invalid contact email + missing address Expected: 422 validation response with field-level errors. Actual: 200 OK returned while the UI shows checkout failure. Risk: Frontend and backend disagree about whether the order was accepted.
Good fit
- You are releasing new endpoints or backend behaviour
- The frontend depends heavily on API states and errors
- Developers need exact request and response evidence
- You want backend checks before UI testing hides the real cause
Not the best fit
- There is no documentation, endpoint access or safe test environment
- You only need load testing or performance benchmarking
- You need a formal security audit instead of product QA
How it usually runs
1
Map the flow
Identify endpoints that support the release, integration or product risk.
2
Test requests
Check valid, invalid, boundary and permission-based scenarios.
3
Compare behaviour
Check whether the UI and API tell the same story.
4
Document evidence
Provide request and response examples developers can inspect quickly.
Related examples
A few useful pages that show how this kind of work is reported.
FAQ
Do you need source-code access?
Not always. Many API checks can be done through docs, staging endpoints, Postman and safe test accounts.
Can API testing be combined with manual QA?
Yes. That is often the best approach when user flows depend heavily on backend state.
Can you help with Postman?
Yes. I can review, structure or improve Postman requests and useful assertions.
Need API behaviour checked before release?
Send the API docs, staging endpoint or product flow that needs validation.