HTTP GET / POST Helper Class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net;
using System.Xml.Linq;
using System.IO;

namespace APIHelper
{
    public static class APITool
    {
        /// <summary>
        /// Generic utility method to build a query string from a dictionary
        /// </summary>
        /// <typeparam name="TKey">Query string variable to be assigned a value</typeparam>
        /// <typeparam name="TValue">Query string value to be assigned to the key</typeparam>
        /// <param name="dict">Dictionary<TKey, TValue> to be passed to the program</param>
        /// <returns>Returns a completed query string, in the form key1=value1&key2=value2</returns>
        public static string BuildQueryString<TKey,TValue>(Dictionary<TKey, TValue> dict)
        {
            //empty query string
            string queryString = "";
            //loop over a key:value pair (hashtable, dict, etc) and build a query string
            foreach (KeyValuePair<TKey, TValue> d in dict)
            {
                queryString += d.Key + "=" + d.Value + "&";
            }
            //Remove trailing & character
            return queryString.Substring(0,queryString.Length-1);
        }

        /// <summary>
        /// Sends a GET request to the URI passed to the constructor.
        /// </summary>
        /// <param name="queryString">Accepts an optional parameter, queryString, which contains a query string of values</param>
        /// <returns>Returns a response from the webserver as a string</returns>
        public static string GET(string uri, string queryString=null)
        {
            WebClient getRequest = new WebClient();
            return getRequest.DownloadString(new Uri(uri + "?" + queryString));
        }

        /// <summary>
        /// Sends a POST request to the URI passed to the constructor
        /// </summary>
        /// <param name="queryString">Accepts optional parameter, queryString, containing a query string to be sent to server</param>
        /// <returns>Returns response from webserver as a string</returns>
        public static string POST(string uri, string queryString = null)
        {
            //New HTTP Request to the URI
            HttpWebRequest postRequest = (HttpWebRequest)WebRequest.Create(new Uri(uri));
            //Response from server
            string response;

            //Convert query string to UTF-8
            byte[] data = Encoding.ASCII.GetBytes(queryString);

            //Set up headers of post request
            postRequest.Method = "POST";
            postRequest.ContentType = "application/x-www-form-urlencoded";
            postRequest.ContentLength = data.Length;
            //Open a stream to write the data
            using (Stream stream = postRequest.GetRequestStream())
            {
                stream.Write(data, 0, data.Length);
            }
            //Get response from server and return it as a string
            using (HttpWebResponse HTTPResponse = (HttpWebResponse)postRequest.GetResponse())
            using (Stream stream = HTTPResponse.GetResponseStream())
            using (StreamReader reader = new StreamReader(stream))
            {
                response = reader.ReadToEnd();
            }

            return response;


        }

    }
}