Is it the migrator's responsibility to ensure a duplicate does not exist on the target site? Maybe, at the very least, check for an identical title?

I intentionally did not offer any specific means of resolving this. In the event of an exact duplicate, the question could be automatically closed/merged while citing the duplicate and preserving links. I agree, the question should not be deleted.

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    @ IAbstract Can I encourage you to switch the accepted answer to Shog9's? This is an old thread and there's more value in having the accepted answer point to the working code than to policy suggestions.
    – E.P.
    Commented Nov 9, 2021 at 9:06

3 Answers 3


This was implemented about two months after it was requested, and apparently never documented.

A migration will be automatically blocked if...

  • ...An exact, word-for-word duplicate already exists on the destination site, or...
  • ...A question created within a week of the one being migrated exists on the destination site with the same author and very similar body text.

Moderators can override this restriction, to allow for the sorts of migrate->close/merge scenarios Michael describes - however, it is important that they coordinate with moderators on the destination site when doing so to avoid confusion.

  • By ".An exact, word-for-word duplicate" you mean title only, right? It doesn't check the body? Commented Mar 17, 2014 at 7:43
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    Title and body, @Shadow. Exact.
    – Shog9
    Commented Mar 17, 2014 at 7:49
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    “Moderators can override this restriction” — how does this work? I've never noticed anything, and I'm sure I've accidentally migrated questions from Computer Science to Stack Overflow which had been dual posts. Do you mean that moderator-initiated migrations simply don't go through these checks? Commented Mar 17, 2014 at 12:59
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    It would make a lot more sense to me to go through with the migration and automatically close one of the copies as a duplicate of the other. Rejected migrations are cumbersome because there's no indication of why the migration was rejected. Why was this not done by automatic duplicate closure (or even merging)? Commented Mar 17, 2014 at 13:01
  • Like I said, you're probably going to want to coordinate with folks on the destination site to make sure this gets done right, @Gilles. If there are answers / comments / edits / votes on both questions, which way should the merge be done? Figure that out before you migrate, if possible.
    – Shog9
    Commented Mar 17, 2014 at 15:11
  • @Shog9, That's odd, how could questions be byte-for-byte exact? Even if the same author had copy and pasted it, wouldn't there be at least whitespace differences?
    – Pacerier
    Commented Feb 27, 2015 at 17:14

I specifically encourage people to migrate exact duplicates to the other site. A mod there can merge it and delete, so then following the migration link will lead straight to the duplicate on the other site

  • Good enough - no broken links!
    – IAbstract
    Commented Jul 6, 2011 at 16:49

I'd say no. The mods and users of the target site would best be able to recognize if something was an exact duplicate or had some unique insight/requirement that justified leaving it open. I imagine providing a moderator flag that it had been migrated from X to Y would be more than enough to ensure it is closed if a duplicate.

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