Top 20 NuGet validation Packages

Model Validation Framework
A library that provides validation capabilities for WinForms controls. Fluent, customizable and easily expandable
Validator is a validation library.
A class invariants helper library
Library to simplify runtime checking by using code contracts.
Visual Studio solution structure and settings validator.
Extension methods for .Net classes
DDD Library for validate your entities according Vaughn Vernon
generator and validator for spanish NIE/NIF numbers
A schema generator that uses DataAnnotations for use in client-side applications.
The specification Pattern is a great way to validate complex business rules in Domain.
Library to Validate special characters in Request and Response
A really simple C# guard clause/validation library
Model Validation for Universal Apps through delegate method invocation per-property or DataAnnotation styled attribute validation. Universal apps targeting Windows 8.1 and Windows Phone 8.1 lack built in, easy to use data Validation, so ValidatableBase was created.
Attribute validation package for WCF
API Validation support with FluentValidation for frameworks we use. Standard error response DTO.
The validation library for the "More" framework.
The base library for all BigEgg's projects.
Validierungen von eXTra 1.3-Dokumenten für das GKV-Kommunikationsserver-Verfahren
Basis-Definitionen für die Validierung von eXTra-Dokumenten