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The standard structure of a question URL is:


It is however not clear if this question-id is unique across all stackexchange sites or is it unique per site. I have tried to find two questions on two different sites with the same id, but so far I haven't been able to (which is what promoted this question).

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up vote 2 down vote accepted


Generally speaking, no ids are unique across sites.

There are some situations where they line up (like linked meta user ids to their parent site user ids), or places where an id series is shared within a site (question_id and answer_id won't collide on Stack Overflow, for example); but these are basically implementation details, unless called out in the documentation you shouldn't rely on them.

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