HtmlHelper.cs

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;

namespace HtmlSerializer
{

    public sealed class HtmlHelper
    {
        private static readonly HtmlHelper _instance = new HtmlHelper();

        public string[] AllTags { get; private set; }
        public string[] SelfClosingTags { get; private set; }

        private HtmlHelper()
        {
            AllTags = JsonSerializer.Deserialize<string[]>(File.ReadAllText("HtmlTags.json"));

            SelfClosingTags = JsonSerializer.Deserialize<string[]>(File.ReadAllText("HtmlVoidTags.json"));
        }

        public static HtmlHelper Instance => _instance;

        public bool IsSelfClosing(string tagName)
        {
            return SelfClosingTags != null && Array.Exists(SelfClosingTags, t => t == tagName);
        }
    }
}