Get Json Data from a URL

public string Getjsondata(string URL)

    {

        System.Net.HttpWebRequest request = null;

        StreamReader responseReader = null;

        string responseData = "";

        try

        {

            request = (System.Net.HttpWebRequest)System.Net.HttpWebRequest.Create(URL);

            responseReader = new StreamReader(request.GetResponse().GetResponseStream());

            responseData = responseReader.ReadToEnd();

        }

        catch

        {

            throw;

        }

        finally

        {

            request.GetResponse().GetResponseStream().Close();

            responseReader.Close();

            responseReader = null;

        }

        return responseData;

    }

Explanation:
  The above method gets the JSON Data form the Url which is passed to the method. Json Data is usually a string in the format of name and value.

The example of json string 


{ "FirstName":"Madhan","LastName":"Kumar" }


How To Find the json string is correct or valid?
For this there are online tools called json parser in which u can paste the string and you can check whether the json  string is correct.
The favourite json Parsers are
http://jsonlint.com/
http://json.parser.online.fr/