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Read More →Sample API testing interview questions and answers from Uncodemy — covering HTTP methods, status codes, authentication, response validation, negative testing, idempotency and tools like Postman and REST Assured.
All three PDFs are free to download — no form, no sign-up.
Three PDFs, each covering a different level of interview preparation. Click the sticky download button to get started.
The complete set of API testing interview questions in one PDF: HTTP methods, status codes and headers, authentication and authorisation, response validation, negative testing, idempotency, and tools like Postman and REST Assured. For anyone preparing end-to-end for an API testing interview.
Foundational interview questions with clear answers: GET, POST, PUT, PATCH and DELETE, 2xx/3xx/4xx/5xx status codes, headers, authentication methods (API key, Basic, Bearer, OAuth 2.0), and what to validate beyond the status code. For freshers and junior testers.
Advanced interview questions for experienced testers: negative and edge-case testing, schema validation, idempotency, chaining requests, token management, automation with Postman and REST Assured, and integrating API tests into CI/CD pipelines. For mid-level and senior testers.
Across companies and roles, API testing interviews tend to test the same core areas. Prepare these five and you'll cover most of what comes up.
GET, POST, PUT, PATCH, DELETE and their expected behaviour. When each status code (200, 201, 204, 400, 401, 403, 404, 500) should be returned, plus common headers like Content-Type and Authorization.
API keys, Basic auth, Bearer tokens, OAuth 2.0, JWT, and the difference between authentication (who you are) and authorisation (what you can do).
Response body fields and data types, schema, headers, response time, error messages for invalid input, and that returned data matches what the system stored.
Missing required fields, invalid formats, duplicate values, oversized input, wrong content type, missing or expired tokens, and unauthorised roles.
Postman collections, environments and tests, REST Assured with Java, Newman for CLI runs, and how API tests fit into CI/CD pipelines (GitHub Actions, Jenkins, GitLab CI). Interviewers want to see that you can automate at scale, not just click in a UI.
These are the kinds of questions the PDFs cover in detail. Read each answer, then practise explaining it in your own words with an example.
PUT replaces a resource with the data sent, while PATCH applies a partial update to some fields. PUT is idempotent; PATCH may or may not be, depending on how it is implemented.
Tip: mention idempotency explicitly401 Unauthorized means authentication is missing or invalid. 403 Forbidden means the caller is authenticated but not allowed to perform the action.
Tip: give a real scenario for eachThe response body fields and data types, the schema, headers such as content type, response time, error messages for invalid input, and that the data matches what the system stored.
Tip: list at least four validationsMissing required fields, invalid formats, duplicate values, oversized input, wrong content type, missing or expired authentication, and unauthorised roles.
Tip: organise tests by categoryAn operation is idempotent if repeating it gives the same result. GET, PUT and DELETE are meant to be idempotent, while POST usually is not.
Tip: give an example of why it mattersPOST usually creates a resource and is not idempotent. PUT replaces a resource at a known address and is idempotent.
Tip: connect this to idempotency questionsTest valid credentials, missing and invalid credentials, expired tokens and users with insufficient permissions, and check the correct status codes are returned.
Tip: mention 401 vs 403 explicitlyJSON schema validation checks that the response body matches an expected structure — required fields, data types, formats and constraints. It catches breaking changes early and prevents tests from silently passing when the API shape drifts.
Tip: mention breaking changes and versioningUse collection variables or environment variables to store values from one response (like a token or an ID), then reference them in later requests using {{variable}} syntax. Use the Tests tab to extract values from the response and set them as variables.
Tip: name the scripting hooksRun your Postman collection using Newman or your REST Assured test suite using Maven/Gradle inside the CI pipeline. Trigger runs on every pull request or on a schedule, report results back to the pipeline, and fail the build if critical tests fail.
Tip: mention Newman, Jenkins, GitHub ActionsThese are the habits that separate candidates who can explain concepts clearly from those who can only recite definitions.
Every PDF in this download set is built around the same core topics and tools used in real API testing interviews.
These PDFs are designed for anyone preparing for an API testing interview — whether it's your first role or a move into a more senior position.
Graduates preparing for their first API testing or QA interview and needing clear, correct answers on core concepts.
Start with Fundamentals PDFManual testers transitioning into API testing who already understand testing basics but need to sharpen their API-specific answers.
Start with Complete Bank PDFAutomation testers adding API testing to their portfolio and preparing for interviews that test tool-specific depth.
Start with Advanced PDFSDET and QA engineering candidates who need to defend architecture and CI/CD decisions around API testing.
Start with Advanced PDFDevelopers who build APIs and want to understand how their work is tested by QA teams, plus how to write better tests themselves.
Start with Complete Bank PDFWorking professionals moving into QA or testing roles who need a structured, credible way to explain API concepts in interviews.
Start with Fundamentals PDFThese are the roles where API testing interview questions from this set most directly apply.
| Role | Core topics tested | PDF to use |
|---|---|---|
| API Tester | HTTP methods, status codes, validation, negative testing | Complete Question Bank |
| QA Engineer | Methods, status codes, auth, response validation | Complete Question Bank |
| Automation Test Engineer | Postman, REST Assured, CI/CD integration | Advanced |
| SDET | All topics plus automation strategy and tooling depth | Advanced |
| Backend Developer | API design, validation, idempotency, security | Fundamentals |
| QA Lead | Test strategy, coverage, automation, CI/CD, contract testing | Advanced |
If your interview is about a month away, this is a simple way to use the PDFs in order.
Read the Fundamentals PDF. Learn to explain each HTTP method, when each 2xx/3xx/4xx/5xx status code is returned, and what each common header does.
Study authentication methods and how to validate responses beyond the status code. Practise a full auth + validation scenario out loud.
Work through negative test categories and practise describing a Postman collection you've built. Be ready to talk about REST Assured and CI integration.
Use the Complete Question Bank PDF as a mock question set. Practise answering out loud and reviewing where your answers slip into jargon without examples.
More study material and guides that pair with these interview questions.
Prefer guided learning? Explore Uncodemy's Software Testing course and prepare for API testing interviews with real trainers — live sessions, real projects and a capstone portfolio you can show in interviews.
These PDFs are study material for learning and revision. They are not a certificate, a degree or a promise of a job, and technology changes, so check official documentation for the latest details.
Spot an error? Write to info@uncodemy.com and the trainer team will review it.
Everything you need to know before using these interview questions.
Common topics are HTTP methods, status codes, authentication, response validation, negative testing, idempotency and tools such as Postman or REST Assured.
401 means authentication is missing or invalid. 403 means the user is authenticated but does not have permission.
POST usually creates a resource and is not idempotent. PUT replaces a resource at a known address and is idempotent.
Test valid credentials, missing and invalid credentials, expired tokens and users with insufficient permissions, and check the correct status codes are returned.
No. They are written to cover common concepts. We do not claim any specific company asked them.
PUT replaces a resource with the data sent, while PATCH applies a partial update to some fields. PUT is idempotent; PATCH may or may not be, depending on how it is implemented.
The response body fields and data types, the schema, headers such as content type, response time, error messages for invalid input, and that the data matches what the system stored.
Manual API testing roles need less coding, but automation-focused roles (SDET, automation test engineer) expect familiarity with at least one language — typically Java, Python or JavaScript — plus a tool like REST Assured or Postman with scripts.
A Postman collection with chained requests and validations, or a REST Assured test suite wired into CI, works well. Be ready to explain what you validated, how you handled authentication, and what bugs you caught.
Yes. All three API Testing interview question PDFs on this page are completely free to download. No sign-up, payment or form is required — just click the sticky download button on this page.
Grab the API Testing interview questions PDF and work through the sample answers at your own pace. All three PDFs are free to download — just use the sticky download button.
