Using FluentValidation?

Short answer: Install FluentValidation.AspNetCore Create a validator class: public class UserValidator : AbstractValidator<User> {

Example code

public UserValidator() {
RuleFor(x => x.Email).NotEmpty().EmailAddress();
}
} Register with: services.AddFluentValidationAutoValidation(); ✅ Offers more readable and testable validation logic than data annotations.

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.