This sort of validation you can immediately return to the client and does not require any sort of domain-specific knowledge.
A next-level validation is domain validation, or as I've often seen referred, "business rule validation".
These are easily translatable to client-side validation rules.
If it were 100 years ago, this would be a desk clerk just making sure you've filled in all the boxes appropriately.
However, I do try to design my UX so that the user cannot get themselves in an invalid state.Before I get into different patterns, I like to make sure I understand the problem I'm trying to solve.In the above picture, from the external request perspective, I need a few questions answered: Think of request validation as "have I filled out the form correctly".There always seem to be some variations here and there.My applications also tend to have explicit objects for external "requests", which are the types bound to the HTTP request variables.But I'm far more concerned with clean code than OOP.