Stop 08 · API TestingTopics · 1/9

REST API Basics for Testers

In short

Behind every app screen, the front end is quietly asking a server for data. Test that conversation directly and you find bugs faster than clicking through the UI ever could.

Understanding how REST APIs work — resources, endpoints, and standard conventions — essential since API testing often catches issues faster and more reliably than testing through the UI alone.

The purple blob hands a token through a canteen window and receives a plate of food.

Think of it like this

The canteen token window

You don't walk into the canteen kitchen. You go to the window, hand over a token saying 'one veg thali', and a plate comes back. An API is that window: a fixed place, a clear request format, and a predictable reply.

Watch it happen

One REST request, start to finish

Tester

API server

Database

GET /posts/1

1/5The tester asks for one resource: post number 1. GET means read only.

The big ideas

What you need to know

Resources and URLs

Each thing has an address: /users, /users/7, /users/7/orders. Nouns in the URL, not verbs.

Request and response

A request has a method, URL, headers and maybe a body. A response has a status, headers and a body.

JSON is the language

Most REST APIs send JSON: key and value pairs that look a lot like a Python dictionary.

Faster than the UI

API tests skip browsers and screens, so they run in milliseconds and break less often.

See it in code

Walk through the code

http

1GET https://jsonplaceholder.typicode.com/posts/12Accept: application/json3 4HTTP/1.1 200 OK5Content-Type: application/json; charset=utf-86 7{8  "userId": 1,9  "id": 1,10  "title": "sunt aut facere repellat provident ...",11  "body": "quia et suscipit ..."12}

1/3Method plus URL, and a header saying we want JSON back.

A real request to JSONPlaceholder, a free fake API for practice, and its response (text shortened).

Save yourself the pain

Common mistakes

Oops

Only checking that the status is 200 and calling it done.

Do this instead

Also check the body: the right fields, types and values for this request.

Oops

Thinking API testing needs the UI to be finished first.

Do this instead

APIs are often ready before screens. Test them early and catch bugs sooner.

Your mission

Read an API in your browser

~15 min

Quick check

Which URL best follows REST style for 'get all orders of user 7'?

Go deeper

1Read a simple REST API's documentation and identify its key endpoints.
2Learn the basic REST conventions: resources represented as URLs, actions represented as HTTP methods.
3Understand why API testing tends to be faster and more stable than UI automation.