I have noticed several cases when a post is linked in a question (or in an answer, in a comment, in a duplicate banner) and yet it is not among linked questions (displayed in the sidebar). I do not mean immediately - I know that it sometimes takes some time. I am speaking about links which have been there for months or years and yet they are not shown.

I will list some examples below - they come mostly from the sites I visit often. (If there is some kind of SEDE magic which could help to find other such situations, I'll be glad to learn about that.)

I have these questions:

  1. Why does this happen? (Is it only in case of old questions before linked questions in the sidebar were implemented? If age of post/comment can be a factor, when did this change? In the case of MathOverflow, can this be caused by migration process to SE network?)
  2. How can this be corrected? (Can the linked questions be updated by some automated process. If not, what could I do when I see such situation and I think that the linked question is important enough to have higher visibility and should be shown in the sidebar.)
  3. What can I do to prevent this. (If this is intended behavior in some situations, how can I make sure that my link will appear among linked questions?)

Here are some examples. I have added Internet Archive links - so that this can be checked if the situation changes.

  • In here pretty sure the reason is using "raw" HTML instead of markdown to post the link. (in the answer) Commented Nov 27, 2016 at 7:12
  • Here it was probably posted too long ago, before Linked Questions even existed. I'm pretty sure that any edit to the question will cause the question to appear as Linked. Commented Nov 27, 2016 at 7:14
  • BTW, your first example is showing up on the side for me.
    – Mithical
    Commented Nov 27, 2016 at 9:02
  • @Mithrandir It is showing for me, too. Either I did not see it or it was not the case when I was posting the question here. But at least you can check that it was not shown a few weeks ago, see here and here.
    – Martin
    Commented Nov 27, 2016 at 9:07
  • 2
    @Mithrandir it's showing because I made a test, posting the link as markdown, then deleted it. Commented Nov 27, 2016 at 10:37
  • Note that apart from the missing database reindexing bug (which is never resolved), there's another bug that nowadays HTTP links are not indexed. Previously HTTPS is broken, and the posted regex suggests that both should work.
    – user202729
    Commented Feb 24, 2021 at 7:26
  • note that URL in code section like https://meta.stackexchange.com/questions/361357/what-is-the-correct-way-to-insert-images-to-stack-posts are still linked
    – user202729
    Commented Feb 24, 2021 at 7:26

2 Answers 2


Most of those are not bugs, as far as I can see. I'll elaborate.

First of all, the Linked Questions feature was added in April 26, 2010 as announced in this blog post. The feature was not retroactive, i.e. it did not go over all existing links, so any link posted before that in a question, answer, or comment, did not cause the target to be linked. (Same for closing as duplicate.)
This explains the lack of Linked Questions here, here, and here.

Second, as reported in Questions don't link if the URL uses HTTPS there was a long time bug that caused https:// links to not be picked, and it was fixed only in February 2015, and like the original feature implementation, it did not check existing links.

As for the example here this looks like a bug indeed, I was not able to find a way to reproduce.

  • Sandbox is showing as linked
    – Cai
    Commented Nov 27, 2016 at 11:08
  • @Cai I know, edited. (it was a live test, since I couldn't use sandbox itself as it already got the max 50 linked questions.) Commented Nov 27, 2016 at 11:08

I asked a question like this on meta.puzzling.

The answer was basically that it had the link as q/number instead of site.stackexchange.com/q/number(/name-of-question).

This doesn't explain all of them, but it should certainly account for some of them.

  • I do not think this is the case. I will add here link to this answer in the form http://meta.stackexchange.com/a/280358. Based on the regex shown in that answer, I believe the question should appear in the sidebar. EDIT: If you check the sidebar now, the question "Why aren't protocol relative links recognized as linked questions?" is indeed there.
    – Martin
    Commented Nov 27, 2016 at 8:30
  • @Martin Sorry, I summarized the answer incorrectly. What if I link something like this?
    – Mithical
    Commented Nov 27, 2016 at 8:35
  • I cannot see source of your comment. How did you format the link? As http://meta.stackexchange.com/q/283949/? Or simply as /questions/283949/ or /q/1? Or as //meta.stackexchange.com/q/283949/?
    – Martin
    Commented Nov 27, 2016 at 8:37
  • @Martin Like /q/283949/.
    – Mithical
    Commented Nov 27, 2016 at 8:38
  • Hmm, now it's showing up. Interesting.
    – Mithical
    Commented Nov 27, 2016 at 8:39
  • You are right that such link are ignored when compiling linked questions, as explained here. I do not think that examples provided above are of this nature, since not many users know about this syntax.
    – Martin
    Commented Nov 27, 2016 at 8:40
  • It's possible that it's showing up now because of my comment. The software probably does not check whether the link is in backticks or not. I will randomly add /q/287411/ link here in comment, I guess it will not be shown.
    – Martin
    Commented Nov 27, 2016 at 8:43

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