For simple cases, examining your response headers "by hand" may suffice:
(1) telnet to the host and port where the server is running - e.g.
        telnet www.myhost.com 80
(2) Enter HTTP request.   The most useful for this purpose is usually HEAD; eg
        HEAD /index.html HTTP/1.0
        (optional HTTP headers)
        (followed by a blank line)
Now you'll get a full HTTP response header back.

For complex cases, such as sending a request with headers (as a browser
does) or POSTing a form, this author's free online diagnosis cg-eye is
included in the respective toolkits at
     http://www.htmlhelp.org/tools/
     http://www.webthing.com/valet/
	This combines an offline cgi "linter" with two online services:
	(a) Interactive mode permits you to formulate an HTTP request,
	which is then sent to your server.
	(b) Live mode submits your form, exactly as it gets it from your
	browser.
	In both cases, it will print a detailed report of the transaction,
	and optionally (if the CGI is producing an HTML page) validate it.