In my experience, the only reliable way to design an API is to cycle through "hats" like gradient descent until the API stops changing. There are no shortcuts!

In my experience, the only reliable way to design an API is to cycle through "hats" like gradient descent until the API stops changing. There are no shortcuts! And there are more hats to consider than just frontend and backend. There's security, testability, teachability, performance, upgradability, there are likely many uses for the API, and more. This is why API design is hard.