Cross posting is posting exactly the same question on multiple Stack Exchange sites. This is both a common and a highly problematic practice; splintering answers across the network doesn't help people looking for them, which is all our sites are supposed to be about. Very new users, who've yet to learn our strange ways, are the usual culprits of this. I don't think we can blame them, this is (more or less) acceptable behaviour on every other forum on the internet. Furthermore, I don't think expecting them to know they can flag for moderation attention and ask for the question to be migrated is reasonable.

That said, and while cross posting is strongly discouraged, it's not forbidden. There are often significant overlaps between sites, and a question may very will be on topic on more than one sites. Cases like this aren't always handled consistently. There are some that believe only one copy of the question should exist, and then there are others that don't find the fact that an on-topic question has been posted elsewhere reason enough to close it.

I'm in the first camp when it comes to questions that have been copy pasted verbatim on multiple sites, and on the second for when the poster has gone through the trouble of tailoring each version to the audience of each site. The first category is, I believe, trivial to detect and it's the one I'd like to see automatically rejected by the system. Even in the rare occasion when a copy pasted question happens to be on topic on both sites, copy pasting your question across the network is perceived as rude and abusive behaviour from veterans. And more often than not, cross posts tend to attract an onslaught of downvotes and/or negatively charged comments, regardless of their topicality. We are doing a very poor job educating our new users about the faults of cross posting, but a fantastic job at chastising them for it.

If outright blocking is out of the question, then I think at least an automated warning is in order. Something along the lines of:

It seems you've already posted this on Chemistry. Also posting it on Arqade may not be such a great idea, questions are very rarely on topic on more than one sites. Please check out Arqade's help center to find more details on what questions this site welcomes.


  • Do you believe that the amount of cross-posts happening is currently overloading the community's ability to handle it enough that an automated solution is necessary?
    – Jason C
    May 17, 2015 at 15:24
  • 2
    ​​​​​​​​​​​​​​​@JasonC On Programmers, yes. However, we are a bit special, we seem to be the go to site for people who've hit a question block on SO. I don't know if this is a serious enough situation elsewhere on the network. Nevertheless, I think the divide between what's commonly done around the web, and SE's culture should be addressed. There are some well meaning users who post their question around not knowing that there are better ways to get answers. Seeing them getting the short end of the stick for it is not ok. We should at least be doing something to educate them before they post.
    – yannis
    May 17, 2015 at 15:28
  • For disclosure, I downvoted this not because I am particularly against the idea itself, but because I would rather see an automated flag (as in the link that Shadow posted) than anything visible to the user; under the presumption that the idea itself is necessary and useful.
    – Jason C
    May 17, 2015 at 15:41
  • ​​​​​​​​​​​​​​​@JasonC Heh, if you follow the trail from the comments in maple_shaft's question, you'll end up to this. I don't think a flag is sufficient, however. If the duplicate has already been detected, why not just let the OP know that what they are doing will probably not be well received?
    – yannis
    May 17, 2015 at 15:46
  • This is probably the most embarrassing duplicate ever; I've either commented on or answered the earlier discussions.
    – yannis
    May 17, 2015 at 15:48
  • per my reading of stats provided here, other sites suffer from SO block-hoppers much less than Programmers
    – gnat
    May 17, 2015 at 18:35

1 Answer 1


The workaround for a straight match is too easy; just change one word and no problem.

I conjecture that you'd want a fuzzier match. I'm not an SE developer but I suspect the cost of a potentially resource intensive operation may not be worth the benefit.

Also: Giving this the benefit of the doubt and assuming that it is useful and free, you'd probably want it to silently and automatically raise a flag or something instead so that a mod or the community could deal with it. Since it'd be relatively easy to work around, letting the user know could just get you in a situation where cross-posts still exist but are harder to detect due to the arbitrary differences added to get past the filter (of course, I am hypothesizing that users will prefer to work around rather than to take the advice, which is purely conjecture).

Right now cross-posts seem to eventually be found and handled by the community fairly effectively already, though. At minimum a comment and a link usually ties the info together, although closure may not always happen as often as some would like. It doesn't seem like it's at the point where the community is overloaded and an automated check is needed (although you mention that Programmers is possibly a special case).

Sweet! This is totally a verb!

  • Skip the first and last line maybe? So the usual 0 upvote downvote favorite is skipped and anything they might add at the bottom (this is for legitimate users who actually will follow the rules) May 17, 2015 at 15:25
  • 1
    @ᔕᖺᘎᕊ Maybe, maybe not. Too difficult to discuss without data. You'd want to just observe how (and if) users are working around such a filter for a while before determining the details of the fuzziness, if it's even needed.
    – Jason C
    May 17, 2015 at 15:28

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