A class to ping a Minecraft server for its description, player count and maximum player count. Based on barneygale's PHP code.

MinecraftServerInfo.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Sockets;
using System.Text;
using System.Text.RegularExpressions;

namespace Minecraft
{
    public class MinecraftServerInfo
    {
        const string NonNumericRegex = "[^.0-9]";

        /// <summary>
        /// A class to ping a Minecraft server for its description, player count and maximum player count.
        /// </summary>
        /// <param name="host">Address of server to ping.</param>
        /// <param name="port">Port on which the Minecraft server sits.</param>
        /// <param name="sendTimeout">How long to wait when sending the ping (in milliseconds).</param>
        /// <param name="recieveTimeout">How long to wait when reciving the ping response (in milliseconds).</param>
        public MinecraftServerInfo(string host, int port = 25565, int sendTimeout = 0, int recieveTimeout = 30000)
        {
            HostName = host;
            Port = port;
            SendTimeout = sendTimeout;
            RecieveTimeout = recieveTimeout;

            Refresh();
        }

        /// <summary>
        /// Refresh the data about this server.
        /// </summary>
        public void Refresh()
        {
            //Set up our TCP Client
            TcpClient tcpClient = new TcpClient();

            //Set the timeouts
            tcpClient.SendTimeout = SendTimeout;
            tcpClient.ReceiveTimeout = RecieveTimeout;

            //Reset values
            Online = false;
            PlayerCount = 0;

            try
            {
                tcpClient.Connect(HostName, Port);

                NetworkStream stream = tcpClient.GetStream();

                //Send server list ping
                stream.Write(new byte[] { 0xFE }, 0, 1);

                //Read data into buffer
                byte[] buffer = new byte[256];
                while (tcpClient.Connected)
                {
                    int readBytes = stream.Read(buffer, 0, 256);
                    if (readBytes == 0)
                        break;
                }

                //Check we've got a 0xFF Disconnect
                if (buffer[0] != 255)
                {
                    Online = false;
                }
                else
                {
                    //Server is online
                    Online = true;

                    //Remove the packet ident (0xFF) and the short containing the length of the string
                    buffer = buffer.Skip(3).ToArray();

                    //Decode UCS-2 string
                    string str = System.Text.Encoding.BigEndianUnicode.GetString(buffer);

                    //Split into array
                    string[] parts = str.Split('§');

                    //Set values
                    Description = parts[0].Trim();
                    PlayerCount = int.Parse(Regex.Replace(parts[1], "[^.0-9]", ""));
                    MaxPlayerCount = int.Parse(Regex.Replace(parts[2], "[^.0-9]", ""));
                }
            }
            catch {
                //Online is already set to false.
                //We assume the server is offline if any errors occur.
            }
            finally
            {
                //close the client
                tcpClient.Close();
            }
        }

        /// <summary>
        /// The port being pinged.
        /// </summary>
        public int Port { get; set; }

        /// <summary>
        /// The hostname being tested.
        /// </summary>
        public string HostName { get; set; }
                
        public int RecieveTimeout { get; set; }
        public int SendTimeout { get; set; }


        /// <summary>
        /// Whether we can reach the server or not.
        /// </summary>
        public bool Online { get; set; }

        /// <summary>
        /// The server's MOTD.
        /// This will always be null if Online has never been true. This information is kept after a Refresh.
        /// </summary>
        public string Description { get; set; }

        /// <summary>
        /// Number of online players.
        /// This will always be 0 if Online is false.
        /// </summary>
        public int PlayerCount { get; set; }

        /// <summary>
        /// Maximum number of players for this server.
        /// This will always be 0 if Online has never been true.  This information is kept after a Refresh.
        /// </summary>
        public int MaxPlayerCount { get; set; }
    }
}