The Prettify helper is a utility type that takes an object type and makes the hover overlay more readable. type Prettify<T> = { [K in keyof T]: T[K]; } & {}; It's known by various names - Id, Compute, Unwrap - but each uses this same implementation. It's also not globally available in TypeScript - you'll need to define it yourself using the code above. #Example Let's imagine that you've got a type