Please excuse me if this is already a feature of has already been suggested (I DID do a search but I might have missed something).
It would speed up development if it were possible to choose another option when creating a validation – whether or not to automatically generate the validation message based on the selected validation options. Perhaps this could be a radio button option between a custom message and an auto message. If you have marked an attribute of a model as required, for example, the automatic message could be that “[AttributeName] is required”. The validation options contain all the information necessary for a primitive error message.
As an example, in .NET, there is a DataAnnotations namespace which allows you to mark properties with attributes that can be used to automatically generate error messages based on the attributes and their parameters.
Let me know what you think of this idea.