How to get a JSON string from URL?

Use the WebClient class in System.Net:

var json = new WebClient().DownloadString("url");

Keep in mind that WebClient is IDisposable, so you would probably add a using statement to this in production code. This would look like:

using (WebClient wc = new WebClient())
{
   var json = wc.DownloadString("url");
}

AFAIK JSON.Net does not provide functionality for reading from a URL. So you need to do this in two steps:

using (var webClient = new System.Net.WebClient()) {
    var json = webClient.DownloadString(URL);
    // Now parse with JSON.Net
}