Get WebMethod parameter list

Question

I'm working on a project that call a WebMethod dynamically after validating its parameters by knowing its URL.

Here's my attempt:

[WebMethod]
public string CalledService (string myText, int count)
{
    return myText;
}

and all I know is its URL

http://localhost:29740/OnewayWebserviceCall/WebService.asmx?op=CalledService

I need a function that returns something like {"myText","count"}

I tried to download the URL string and search for the parameters in it but I need something more time efficient.