Custom validation attributes?

Short answer: Create custom rules by inheriting ValidationAttribute: public class MustBeEvenAttribute : ValidationAttribute { public override bool IsValid(object value) { return (int)value % 2 == 0; } } Use like: [MustBeEven] public int Number { get; set; }

Example code

Create custom rules by inheriting ValidationAttribute: public class MustBeEvenAttribute : ValidationAttribute {
public override bool IsValid(object value) {
return (int)value % 2 == 0;
}
} Use like: [MustBeEven] public int Number { get; set; }

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.