There is a policy, stated in the how to answer page which is linked from the FAQ:
Provide context for links
A link to a potential solution is always welcome, but please add context around the link so your fellow users will have some idea what it is and why it’s there . Always quote the most relevant part of an important link, in case the target site is unreachable or goes permanently offline.
If you see an answer which is little more than a link, the acid test is: if the link is not accessible, is the answer still useful?
If the answer is still useful (for example, the question was how to do X, and the answer is a link to a package page on http://packages.ubuntu.com for a program that does X), then it's a valid answer. It's usually not a very good answer — an explanation of why the linked resource applies would be nice — but it is an answer.
If you need to visit the link to get any use from the answer, then it is in fact not an answer and should be removed. Use your best judgement as to what to do with it:
If the link is to another Ask Ubuntu question:
- leave a comment telling the answerer to vote or flag to close the question as a duplicate in such circumstances.
- flag the answer as “not an answer” (or delete it if you're a moderator).
- vote or flag to close the question as a duplicate if you agree.
If the answer is recent, and you think the linked resource is worthwhile, leave a comment citing the answer policy and suggesting that the answerer add some real content and that the answer might be deleted otherwise. I recommend also downvoting the (non-)answer, as this tends to motivate posters to improve their answers; be sure to come back later to check, and transform your downvote into an upvote if the answer has been updated.
If you think the linked resource is worthwhile, and you have the time and knowledge, edit the answer, summarizing the information found behind the link.
If the link is already given by other answers, or the material behind the link is similar to material given in other answers, the link-only answer should be deleted outright. Vote to delete if you can, otherwise flag to delete (use either the generic “not an answer” flag or a custom flag citing the answer that already has the material).
If none of the above applies, flag the answer, either as “not an answer” or with a custom flag suggesting that the answer be transformed into a comment. A link to a place where an answer can be found is best posted as a comment to the question: it provides useful information, but it is does not in itself answer the question (so having it in the answer section is bad, because it gives the false impression that the question is answered).
Note that it's ok to flag a link-only post as not an answer even if you posted a “competing” answer. A moderator will review the flag, so don't worry about a possible conflict of interest. If you're a moderator, you might want to let one of your colleagues handle this — or not, there is no conflict of interest in blatant cases.
