lgclrd

This is a great/simple rule to keep in mind.

Superficial validation on things like form fields still occurs up in the UI layer before a Use Case is invoked. Additional validation is likely to happen in the Use Case as well. It's a ubiquitous thing so just like in any other app it should be happening at a few different points but the stuff validated in the Use Case is going to be related to the business rules it's trying to execute.