validate my web-service.

[Mr. x]

Hello,
In asp I can validate the aspx, by putting the following line at the header
of the aspx :
<%@ page debug = "true" %>

At the same manner, how can I debug a web-service ?
(or what should I put in the head of the web-service ?

Is there any script/free utility which I can debug a specific web-service or
aspx ?
Need code sample, please.

Thanks