API testing: practice, test and prove it

Covers HTTP methods, status codes, headers, JSON, REST, authentication, idempotency and negative tests.

FreeNo sign-up to testNo attempts yet

Start the api testing test Read the first lesson

API testing screenings check whether you understand what travels between a client and a server. Typical questions show a request or a JSON response and ask which status code is correct, which header is missing, or what a good negative test would be. Knowing the meaning behind each method and code matters more than any particular tool.

This page uses a generic API client and plain HTTP examples throughout. The lessons explain requests, responses and REST conventions, then how to validate responses and design negative and authentication tests.

Benchmark: The pass mark on this site is 80%, and API testing is commonly screened for QA engineer, automation tester, SDET and backend support roles. Requirements vary by employer.

Lessons

Requests, responses and REST basics for testersWhat is inside an HTTP request and response, what each method and status code family means, and how REST URLs are structured.Lesson 1

Validating responses, negative tests and authentication checksWhat to check beyond the status code, how to design negative and boundary tests, and how to test API keys and bearer tokens.Lesson 2

Postman collections, environments and test scriptsOrganise requests into collections, keep base URLs and tokens in environments, write pm.test checks and run everything with Newman.Lesson 3

Testing with curl: idempotency, pagination and rate limitsSend and inspect requests from the command line, prove which methods are idempotent, and test paging, limits and 429 handling.Lesson 4

Interview prep

API testing interview questionsAPI testing questions interviewers commonly ask, with answers that show how you design and judge tests.6 questions

Certificate

Free with an accountA PDF with your name, best score and date. Records this site's tests only.

Common questions

Do I need programming skills for API testing?

You can start with an API client and no code. Automation roles usually also expect scripting in a language such as Java, Python or JavaScript.

Is API testing only about REST?

No, but REST over HTTP with JSON is the most common style in screenings. The same habits of checking status, headers and body apply to other styles.

What is the difference between API testing and UI testing?

API tests call the server directly without a browser, so they are faster and pinpoint server-side problems. UI tests check what a user sees and does on screen.

API testing test for interviewWhat the screening round looks like, with a 5-question sample.