D&D Tools.eu has been taken down.
They received a cease & desist letter from Wizards of the Coast. That pretty well settles the debate: we shouldn't link to it, because there's nothing there now. SevenSidedDie's predictions came true.
There's some parting words from the owner on the homepage, and an explanation of the situation: http://dndtools.eu/
If that ever goes down too, the same parting words are preserved on the Internet Archive Wayback Machine.
Speaking of the Wayback Machine: I suggest we do not link to cached/archived versions of D&D Tools.
Legal or moral issues of whether we should link to cached versions entirely aside: those preserved copies of the site's copyright-violating content are going to go away eventually too, and they're broken links simply waiting to be such.
Internet Archive services requests to remove copyrighted works. See their Wayback Machine FAQ, specifically: What is the Wayback Machine's Copyright Policy?
Google Cache has done similar in the past.
Same goes for mirrors: don't link to 'em.
So, there's mirrors now.
Wizards of the Coast will catch up with those too, however many pop up, one by one. While they're busy playing whack-a-mole like world governments with the Pirate Bay, we're going to get the same links breaking along the way, which is a pain.
Just say what you have, cite the book, and rely that whoever's reading might have the book (and really, these are the people you want answering your question anyway because they understand the greater context of your thing). Whoever else can go look up an illegal third party site like dndtools, that's their choice.