Validation Patterns

This walks through the validation layer cake in ASP.NET Core, from DataAnnotations up through FluentValidation and options validation at startup. You get decision trees for picking the right approach (simple attributes vs IValidatableObject vs custom ValidationAttribute), tables of built-in attributes including the .NET 8 additions like AllowedValues and Base64String, and working examples of cross-property validation and MediatR pipeline behaviors. The IValidateOptions pattern for catching bad configuration at startup is especially worth having around. It's comprehensive enough that you'll reference it when setting up validation in a new project or when you need to remember the syntax for custom validators that need database access.

skills.sh installs: 542
GitHub stars: 90
last updated: Aug 21, 2026

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Install

$ npx -y skills add wshaddix/dotnet-skills --skill validation-patterns --agent claude-code

Installs into .claude/skills of the current project.

Files

Validation Patterns in ASP.NET Core

Rationale

Validation is critical for both security and user experience. Poor validation leads to invalid data, security vulnerabilities, and confusing error messages. These patterns provide a comprehensive approach to validation at multiple layers.

Validation Strategy

Layer	Purpose	Technology
Client-Side	Immediate feedback, reduce server load	jQuery Validation, HTML5
Model Binding	Data type/format validation	Model Binders
Application	Business rule validation	FluentValidation, DataAnnotations
Configuration	Startup validation	IValidateOptions
Database	Constraint enforcement	EF Core Configurations