This is a simple validation framework that I created for one of my projects that I am releasing under an open source MIT license.
The framework supports a number of different types of validations including string length, number range, email validation, regex validation and equality.
Validation rules can be added to any keypath of any object that inherits from NSObject, as well as having multiple validation rules per object. Here is a screenshot:
And here is the project on Github - DBValidator