Validation in .NET Core using FluentValidation

Data validation is an important part of guaranteeing data integrity and preventing errors in any application. With the help of FluentValidation, handling data validation in.NET Core apps has become more intuitive and expressive. FluentValidation is a popular package that allows you to build and apply validation rules in a simple and fluent manner. In this blog post, we’ll look at how to utilize FluentValidation to make data validation in.NET Core apps easier.

What exactly is FluentValidation?

FluentValidation is an open-source.NET package that allows for more expressive and maintainable data validation. It’s very prevalent in ASP.NET Core applications where validating user inputs in forms, API queries, or any other data is required. FluentValidation allows you to construct validation rules in a declarative and fluent syntax, making your validation logic simple to understand and manage.

Getting Started with FluentValidation

To get started with FluentValidation in your .NET Core project, follow these steps:

The tools that I used for this sample project.

  1. VS 2022 Community Edition
  2. Web API
  3. FluentValidation NuGet Package
  4. .NET 6.0

Step 1. Install the FluentValidation NuGet Package

Begin by installing the FluentValidation NuGet package in your project. You can use the Package Manager Console or add it to your project file, as shown in the previous section.

Step 2. Create Validation Rules

Next, create validation rules by defining validator classes that inherit from AbstractValidator<T>. These classes specify how the validation should be performed for a particular data type T. For example.

Step 3. Register the Validators in the Program.cs

Register a validator with the service provider.

Step 4. Use Validation in Your Code

In your application code, use the validator to validate your data objects, for example, in an ASP.NET Core controller action.

Step 5. Handle Validation Errors

If validation fails, FluentValidation provides detailed error messages that you can use to populate your ModelState or handle errors in any way you prefer. The IsValid property of the ValidationResult object indicates whether the data is valid or not.

Advantages of Using FluentValidation

FluentValidation offers several advantages when it comes to data validation in .NET Core.

  • Readability: The fluent and declarative syntax makes your validation rules easy to read and understand, even for complex scenarios.
  • Separation of Concerns: By encapsulating validation rules in separate validator classes, you achieve better separation of concerns in your codebase.
  • Reusability: Validator classes can be reused across different parts of your application, promoting code reusability.
  • Customization: FluentValidation provides a wide range of built-in validation rules, but you can easily create custom validators to suit your specific needs.
  • Localization: It supports the localization of error messages, making it easy to create multilingual applications.


FluentValidation is a powerful tool for simplifying data validation in .NET Core applications. It offers a clean and expressive way to define and enforce validation rules, leading to more maintainable and robust code. Whether you’re building web applications, APIs, or any other type of .NET Core project, FluentValidation can help you ensure the integrity of your data and provide a better user experience.

To get started with FluentValidation, simply install the NuGet package and begin creating your validator classes. Your code will become more organized, and your data validation logic will be easier to manage. Happy coding!

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