In this article I will explain with an example, how to implement Client Side validation for CheckBox in ASP.Net Core MVC.
The Client Side validation will be performed for CheckBox using Model, Data Annotations and jQuery in ASP.Net Core MVC.
Custom Validation Data Annotations Attribute for CheckBox
The Required Data Annotation attribute does not work for Boolean validation i.e. performing validation Checked or Unchecked for a CheckBox.
Hence, a new class will be created for developing Custom Validation Data Annotations Attribute for CheckBox. This attribute will validate the CheckBox as Boolean validation i.e. only two values True or False and will raise error when the value is False.
using System.ComponentModel.DataAnnotations;
using Microsoft.AspNetCore.Mvc.ModelBinding.Validation;
namespace CheckBox_Validation_MVC_Core
    public class CheckBoxRequired : ValidationAttribute, IClientModelValidator
        public override bool IsValid(object value)
            if (value is bool)
                return (bool)value;
            return false;
        public void AddValidation(ClientModelValidationContext context)
            context.Attributes.Add("data-val-checkboxrequired", FormatErrorMessage(context.ModelMetadata.GetDisplayName()));
The following Model class consists of one property TermsConditions to which the CheckBoxRequired Custom Data Annotation attribute has been applied.
The CheckBoxRequired Custom Data Annotation has been specified with a property Error Message with a string value. As the name suggests, this string value will be displayed to the user when the validation fails.
public class PersonModel
    [Display(Name = "I accept the above terms and conditions.")]
    [CheckBoxRequired(ErrorMessage = "Please accept the terms and condition.")]
    public bool TermsConditions { get; set; }
The Controller consists of following two Action methods.
Action method for handling GET operation
Inside this Action method, simply the View is returned.
Action method for handling POST operation
This Action method handles the POST operation and when the form is submitted, the object of the PersonModel class is sent to this method.
public class HomeController : Controller
    // GET: Home
    public IActionResult Index()
        return View();
    public IActionResult Index(PersonModel person)
        return View();
Inside the View, in the very first line the PersonModel class is declared as Model for the View.
The Form
The View consists of an HTML Form which has been created using following ASP.Net Tag Helpers attributes.
asp-action – Name of the Action. In this case the name is Index.
asp-controller – Name of the Controller. In this case the name is Home.
method – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
The Form consists of a HTML Input CheckBox, a Label, a SPAN element and a Submit Button.
The Input CheckBox has been assigned with asp-for Tag Helper attribute and its value is set with the TermsConditions property. Thus, this signifies that the validation will be performed for the TermsConditions property.
The Label has been assigned with asp-for Tag Helper attribute and here also its value is set with the TermsConditions property which signifies that it is used for displaying the Model property name.
The SPAN has been assigned with asp-validation-for Tag Helper attribute and here also its value is set with the TermsConditions property which signifies that it is used for displaying the Validation message for the TermsConditions property.
When the Submit button is clicked, the Form gets submitted and the TermsConditions value is sent to the Controller.
Enabling Client-Side validations
By default, the validations performed using Data Annotations and Model class is performed on Server Side.
In order to enable Client-Side validations, you will need to inherit the following script files.
1. jquery.js
2. jquery.validate.js
3. jquery.validate.unobtrusive.js
Once, the above files are inherited automatically the Client-Side validations using Data Annotations is enabled.
Finally, in order to make the CheckBoxRequired Custom Data Annotation validation to work on Client Side, the validation rule needs to be added to the jQuery Unobtrusive Validation Adapters.
@model CheckBox_Validation_MVC_Core.Models.PersonModel
@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
    Layout = null;
<!DOCTYPE html>
    <meta name="viewport" content="width=device-width" />
    <style type="text/css">
        body { font-family: Arial; font-size: 10pt; }
        .error { color: red; }
    <form method="post" asp-controller="Home" asp-action="Index">
                <td><input asp-for="TermsConditions" type="checkbox" /></td>
                <td><label asp-for="TermsConditions"></label></td>
                <td><span asp-validation-for="TermsConditions" class="error"></span></td>
                <td><input type="submit" value="Submit" /></td>
    <!--OPTIONAL: Add the following scripts for enabling Client Side validation.-->
    <script type="text/javascript" src=""></script>
    <script type="text/javascript" src=""></script>
    <script type="text/javascript" src=""></script>
    <script type="text/javascript">
        (function ($) {
            $.validator.unobtrusive.adapters.addBool("checkboxrequired", "required");
Client Side CheckBox validation in ASP.Net Core