Hi @Hikljh Dima, Based on my understanding, the clean architecture is to structure the code in a way that the business logic (core domain) is isolated from external concerns such as frameworks and libraries. While the Clean Architecture principles advocate for keeping the application layer free from dependencies on external libraries, it doesn't mean that you can't use any external libraries at all. It means we need concern the frameworks and libraries impact of the overall architecture. The fluent validation we could consider it works as a tool. You could also write the library to achieve the same thing inside the application layer. Clean architecture doesn't mean don't use any library. The mean goal is to keep the business logic isolated from the technical details and frameworks. If the use of a library is focused on technical concerns like validation or mapping, it might be acceptable.
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