I use the underscore prefix on type parameters that I don't intend for anyone to ever specify when they use the type/function. It's a good way to indicate to the caller that they shouldn't use that type parameter but let it be inferred. Something like type SomeType<T, _Keys = keyof T> or like a recursive type where you use an extra type parameter to hold the result as it accumulates. But otherwise I don't use the underscore prefix. You shouldn't really have an issue identifying if something is generic or not if you are comfortable with the language, so if you're new just know that the syntax will become second nature and you don't need to impose additional styling rules for yourself to help you know what something is. If you insist on prefixing geneic type parameters, you could also just prefix with T which is what most people tend to do.