local m.url,m.Result
m.url="https://www.levelextreme.com/ViewPageGenericLogin.aspx"

DECLARE INTEGER InternetCheckConnection IN wininet   STRING lpszUrl, INTEGER dwFlags, INTEGER dwReserved 
#DEFINE FLAG_ICC_FORCE_CONNECTION  1 

LOCAL llResult 
m.lResult = (InternetCheckConnection(m.URL, FLAG_ICC_FORCE_CONNECTION, 0) = 1)
if m.lResult=.t.
messagebox("Valid URL",0+32+4096,'',1000)
else
messagebox("inValid URL",0+32+4096,'',1000)
endi

see also this:http://www.sourcecodester.com/tutorials/c/7296/url-validation-using-c.html
if you can translate to vfp (regExp)