The Jupyter comparison isn't completely off base if you'd like to rationalise it that way. Similarity would be blending the code and the docs in a single file, where you can then also execute something.

By definition, API Client is a devtool that makes it easier for devs (& co.) to design, test, document, and debug APIs. If it's confusing, we can take it to Postman, but it's an industry standard, been that way for a long while.