In this article I will explain with an example, how to perform Mobile Number (Cellphone Number) TextBox validation i.e. exact Ten Numbers (Digits) validation on Client Side using Data Annotation in ASP.Net Core MVC.
The Mobile Phone Number (Cellphone Number) validation will be performed using Regular Expression (Regex).
The following Model class consists of one property MobileNumber. The property is decorated with the following Data Annotation attributes for performing validations.
1. Required Data Annotation attribute.
2. RegularExpression Data Annotation attribute.
Note: The Data Annotations attributes can be used with the Entity Data Model (EDM), LINQ to SQL, and other data models.
The Required Data Annotation and the RegularExpression Data Annotation attributes have 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 respective validation fails.
The RegularExpression Data Annotation attribute has been set with a Regular Expression for validating Mobile Phone Number (Cellphone Number).
using System.ComponentModel.DataAnnotations;
namespace MobileNumber_Validation_MVC_Core.Models
    public class PersonModel
        [Display(Name = "Mobile Number:")]
        [Required(ErrorMessage = "Mobile Number is required.")]
        [RegularExpression("^([0-9]{10})$", ErrorMessage = "Invalid Mobile Number.")]
        public string MobileNumber { 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.
The state of the submitted Model is checked using ModelState.IsValid property.
Note: ModelState.IsValid property is an inbuilt property which verifies two things:
1. Whether the Form values are bound to the Model.
2. All the validations specified inside Model class using Data annotations have been passed.
public class HomeController : Controller
    public IActionResult Index()
        return View();
    public IActionResult Index(PersonModel person)
        if (ModelState.IsValid)
            // Validation Success.
        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.
Implementing Validation
The Form consists of a Label, a HTML INPUT TextBox, a SPAN element and a Submit Button.
The TextBox has been set with the following Tag Helpers attributes:-
asp-for – The Model property to which validation will be performed. In this case MobileNumber.
asp-validation-for – Displaying the validation message for the Model property.
When the Submit Button is clicked, the Form gets submitted and the MobileNumber value is sent to the Controller.
Enabling Client-Side validations
The default validation performed is server side when one uses Data Annotations along with Model class for validation purpose.
In order to enable Client-Side validations, you 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.
@model MobileNumber_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><label asp-for="MobileNumber"></label></td>
                <td><input type="text" asp-for="MobileNumber" /></td>
                <td><span asp-validation-for="MobileNumber" class="error"></span></td>
                <td><input type="submit" value="Submit" /></td>
    <script type="text/javascript" src=""></script>
    <script type="text/javascript" src=""></script>
    <script type="text/javascript" src=""></script>
ASP.Net Core MVC: Mobile Number (Cellphone Number) Validation using Data Annotations