Simple way

https://our.umbraco.com/Documentation/Reference/Events/ContentService-Events-v7

using System.Linq;
using Umbraco.Core;
using Umbraco.Core.Events;
using Umbraco.Core.Models;
using Umbraco.Core.Services;

namespace Mynamespace
{
    public class ContentEvents : ApplicationEventHandler
    {

        protected override void ApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            ContentService.Saving += ContentService_Saving;
        }

        private void ContentService_Saving(IContentService sender, SaveEventArgs<IContent> e)
        {
            //remove the linq for all
            foreach (var node in e.SavedEntities.Where(x=> x.ContentType.Alias.Equals("MyAlias")))
            {
                //limit
                if (node.Name.Length > 100)
                {
                    e.Cancel = true;

                    e.Messages.Add(new EventMessage("Validation", "my error message", EventMessageType.Error));
                }
            }
        }        
    }
}