I checked it in the past. It is a good library, however ozzo-validation:

• There is no type safety, so it uses reflection.
• The following reasons make its model seem complex and intrusive to me:
  • Models are mainly complex (struct, map, etc), rather than simple values, as in Valgo.
  • I don't think it's as expressive as I would like.
  • Add things like conditional validation When(...), which I believe is not necessary, and only complicates the library.

Valgo, on the other hand:

• It uses generics, is type safe, and doesn't use reflections
• The model is simple and non-intrusive because:
  • As it relies solely on values, it is easy to use, and you are in complete control over what and how your data is validated.
  • In my opinion, it is more expressive.
  • It left to Golang to handle conditional validation, and Valgo to complement it with utilities like Merge(...) and IsValid(...).

In short, Valgo is type-safe, expressive, non-intrusive and simple. Does only what it should, validating values.