Website Debugging Question

A while ago there was a link to a site debugger, I think it was related to w3 but I can’t remember, I’ve been meaning to use it, and I can’t for the life of me remember what it is.
I swear it was dBlue that posted the link, but I just spied his/your posts and I can’t seem to find it. :)

Basically it goes through a site and finds code errors and I think compatibility errors too.
Whatever it did was really good.

also useful/interesting/confusing:

another thing I can’t develop pages anymore is firebug… a firefox add on…
with this you can actually debug a website…

what you described sound really more like a validator…

but with firebug you can actually inspect the code of a website and change it in realtime,
see what elements use the most bandwidth and even debug javascript and + + +

perhaps it helps you, whatever you need to solve… ;)