Course Overview

Welcome to API Testing Fundamentals, a tool-agnostic course about the layer underneath every API testing tool you will ever use.

Most people learn API testing backwards. They learn a tool first (Postman, REST Assured, Playwright, Cypress), get comfortable clicking Send, and only later discover they cannot tell whether a response is correct, whether a 400 should have been a 422, or why their suite breaks every time a developer adds a harmless field. The tool was never the hard part. The protocol and the judgment were.

This course teaches what to test and why, so that any tool becomes a detail.

Who this course is for 👤

1. Manual testers moving into automation, who keep being told that API tests are the best place to start and want to understand them before automating them
2. Automation engineers who learned a tool before the protocol, and can write a request but not defend an assertion in code review
3. Anyone who works next to an API: developers, support engineers, product people who want to read a response and know what it is telling them

No prior API experience is assumed. If you have never sent a request in your life, start here.

What this course is

This is a concepts course. There is no repository to clone, no tool to install, and no code to write. Every lesson is deliberately portable: whatever you learn here applies just as well in Postman, REST Assured, Playwright's APIRequest, Cypress's cy.request(), k6, or plain curl.

That portability is the point. Tools change every few years. HTTP does not.

Its relationship to the Playwright API course 🔗

The platform also has a hands-on course, Basics of API Testing with Playwright, which walks you through automating a real REST endpoint end to end.

The two fit together deliberately:

• This course explains what is worth testing in an API and why an assertion is a good one
• The Playwright course shows how to express those tests in a specific tool, on a real API, running in CI

You can take them in either order, but taking this one first makes the other one much easier: you will already know what a 401 means, why you assert on the schema instead of the exact payload, and what the query parameter tests are really checking.

How this course is organized 🗺️

Twelve lessons, grouped into three parts, then a bonus:

1. How APIs work: HTTP in practice, REST conventions, the anatomy of a request and a response, and authentication
2. Designing API tests: what to assert, schema and contract validation, test data and environment independence, and error cases
3. Working like a professional: exploring an API before testing it, and running API tests in CI

The bonus lesson maps every concept from the course onto the actual tools, so you leave knowing where each idea lands in the tool you use at work.

If you need more ground 📚

Some lessons assume you have seen HTTP, REST, and JSON before. If any of that feels shaky, you do not need to leave the platform: the HTTP, REST, and JSON fundamentals topic covers it, and you can come back here right after.

👨‍🏫 The Fundamentals section is included with your account. Open it in another tab whenever a term goes past you, then keep going.

Quizzes

At the end of every lesson there is a short quiz about the concepts covered.

👨‍🏫 You must score 100% in the quiz to unlock the next lesson.

The questions are deliberately about judgment rather than memorization. You will be asked what an API should return in a situation, not which method is idempotent.

Need help? 🆘

If you get stuck at any point during the course, you can reach out for support directly from the platform.

Look for the chat bubble with a question mark button in the bottom-right corner of any course or lesson page. Clicking it takes you to the Support page, where you'll find my email address, a template to help you describe your issue clearly, and a link to join our private Telegram group - where you can connect with fellow students and get direct support from the instructor whenever you hit a snag.

Share your feedback 💬

Got an idea to make this course - or the platform - even better? A topic you wish we covered, or a whole new course you'd love to see? I'd love to hear it.

Look for the chat bubble with a plus sign button in the bottom-right corner of any course or lesson page, just above the support button. Clicking it takes you to the Feedback page, where you can send your suggestions, improvement ideas, or course requests through a quick form.

💡 Every bit of feedback helps shape what comes next. Thank you for taking the time to share it!

Let's get started 🚀

That is everything you need to know to begin.

This overview is free to read without an account, so feel free to share it with anyone who is about to start testing APIs.

👨‍🏫 Head over to the next lesson to see why API tests are worth your time in the first place.