Is there an inline class for form attributes validation in Blazor? How do you define the validations in Razor component files?

You can define the form attribute validation in a Razor component inside the function to achieve this. Please do not forget to include the DataAnnotations in the Razor component file.

@using System.ComponentModel.DataAnnotations;

<EditForm Model="@model" OnValidSubmit="@SubmitHandler">
    <DataAnnotationsValidator />
    <ValidationSummary />

    <div class="form-group d-flex justify-content-between">
        <label class="col-form-label col-3" for="name">Name</label>
        <InputText @bind-Value="@model.Name" id="name" Class="form-control" />
    </div>
    
    <button type="submit" @onclick="@SubmitHandler" class="btn btn-primary">Submit</button>
</EditForm>

@code {
    public class ModelClass
    {
        [Required]
        public string Name { get; set; }
    }
    private ModelClass model = new ModelClass();
    private void SubmitHandler()
    {
        Console.WriteLine("Submit");
    }   
}

Please refer to this documentation for more form validations.