Sometimes one might ask a question on a website such as Mathematics Stack Exchange which is comparable but not identical to MathOverflow, and then decide to post the same question on MathOverflow. This practice is called cross-posting between different sites.

Is cross-posting discouraged? When is it okay to cross-post?

  • 6
    $\begingroup$ My understanding is that if a question is posted to MSE and receives no/very little response after about a week (but hopefully gets upvotes), it’s appropriate to repost on MO if the question is borderline research level. $\endgroup$
    – Alec Rhea
    Commented Apr 23, 2021 at 23:07
  • 4
    $\begingroup$ If that was the intention, maybe the tag (faq-proposed) or (faq) could be added to this question. (IIRC the latter can only be added by a moderator.) $\endgroup$ Commented Apr 24, 2021 at 14:58
  • $\begingroup$ @MartinSleziak I think this is a good idea. I will go ahead and add faq-proposed for now with the intention of adding faq later. As you also suggested in chat, it may also be appropriate to add this question to this page on cross-posting. $\endgroup$
    – Tim Campion Mod
    Commented Apr 24, 2021 at 15:01
  • $\begingroup$ @MartinSleziak I added the faq tag and accepted your proposed edit on the cross-posting tag info. Thanks! $\endgroup$
    – Tim Campion Mod
    Commented Apr 28, 2021 at 17:07

1 Answer 1


Cross-posting is discouraged in general, because it can lead to duplication of effort by people answering on different sites. However, it is appropriate under some circumstances.

Most of the advice discussed by Joonas Ilmavirta in the context of cross-posting to Math Stack Exchange is applicable in general. To quote Joonas, if you're considering cross-posting, you should do the following:

  1. Wait several days, not just hours. I would suggest a week.

That is, it is only appropriate to cross-post if you have waited some time after your first post and have not received any answers or have received only unsatisfactory answers. Be patient, and wait for results before cross-posting.

  1. Provide links between the two versions. The MO question should have link to the one at MSE [or other site] and vice versa. (This is for honesty and avoiding duplicate efforts for those who answer.)

You should be up-front about the fact that you are cross-posting. This helps others to see what progress has been made and provides context for your question.

  1. Make sure the question is on-topic at the new site.

This applies to all questions, not just cross-posted ones.

  1. If you have received helpful comments for the old question but no answers, take them into consideration when posting here.

Do not simply copy and paste the old question from one site to another. Revise to to reflect what you have learned so far.

  1. MO and [other sites such as] MSE require different merits for questions to be well-received. Not only are the scopes different, but also the communities value different kinds of background information.

As a corollary, you should revise your post to meet the norms of the community you are cross-posting it to.

You should not cross-post instantaneously. If you realized that you asked in the wrong place and there are no answers yet, simply delete the old one and ask in the right place.

However, if you have received comments or answers on your question, it is rude to delete the old question and cross-post elsewhere.

Finally, you should also consider the policies of the other site you're posting to regarding cross-posting. For example, Mathematics Stack Exchange has guidance on cross-posting between their site and MathOverflow.

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    $\begingroup$ I'd add another reason for linking each post to the other. A user who regularly visits only one of the two sites may find that information on the other site is exactly what she needs in order to come up with a good answer. $\endgroup$ Commented Apr 24, 2021 at 6:24

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