Today I commented on a question if the OP knew what the definitions of a question were. (The question was on group theory and knowing the definitions was an important part of the question).

I went back a while later and it had disappeared.

That comment was of course inconsequential, but I fear that some administrator might be deleting a bunch of comments from various users on a whim. This is a bit troubling as there is no notification for when your comment is deleted.

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    $\begingroup$ Do you mean your deleted comment on this question? You actually deleted it yourself. $\endgroup$ Oct 10, 2017 at 5:55
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    $\begingroup$ yes, I do. I did? $\endgroup$
    – user33907
    Oct 10, 2017 at 6:03
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    $\begingroup$ Yes, when I click to show deleted comments, it shows your comment and "deleted by Jorge Fernández 57 mins ago". $\endgroup$ Oct 10, 2017 at 6:09
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    $\begingroup$ Well, this is embarrassing. Jorge is having trouble recovering his sanity. Sorry for bothering you. $\endgroup$
    – user33907
    Oct 10, 2017 at 6:11
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    $\begingroup$ No problem. That being said, the threshold for deleting comments is fairly low. For example, if the question would be edited to include information that shows OP is aware of the relevant definitions, I might have deleted it after getting a "no longer relevant"-comment-flag. There are also cases where comment threads get too long and are cleared up. $\endgroup$ Oct 10, 2017 at 6:14
  • $\begingroup$ @MichaelGreinecker Do I remember correctly, that a comment can be deleted also by regular users - not only by moderators - if it gets enough flags? Also is the type of flags relevant? (Would several "no longer needed" flags cause deletion, or it works this way only if the comment would be flagged as spam or rude/abusive by several users?) $\endgroup$ Oct 10, 2017 at 6:43
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    $\begingroup$ There is this post on meta.SE: Reduce the threshold for comment deletion with flags. It mentions three flags, but the comment linked there says that it might be higher if the comment was upvoted. But unless I missed something, there is no mention where the type of flag plays a role here. (And the post is from 2015, things might have changed since then.) $\endgroup$ Oct 10, 2017 at 6:47
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    $\begingroup$ @MartinSleziak I think "offensive"-flags work faster, but I'm not sure. $\endgroup$ Oct 10, 2017 at 6:57
  • $\begingroup$ @MichaelGreinecker Thanks for your response, I have posted a separated question about this (here on our local meta): What are details of deleting comments by flags from regular users? $\endgroup$ Oct 10, 2017 at 7:05

1 Answer 1


The specific case has been explained in the comments, but let me remark on comment deletion in general. I am a regular user on this site and a moderator on another SE site.

Comments are second class content on all SE sites. A comment can recommend clarification or other edits, and the comment is obsolete once the post has been edited accordingly. If the OP does not respond to the comment, you can consider making the relevant edit yourself — within reason. Answers, no matter how simple, should be posted as answers, not comments.

Do not put anything valuable in comments. Valuable content belongs in questions and answers. Comments are transient notes that are supposed to help improve questions and answers. The threshold for deleting comments is low, and this is on purpose; they are a sidetrack to the actual Q&A activity.

Admittedly, there are insightful or otherwise useful comments that one might prefer to keep. But even then, it would typically be better to incorporate the comment into the commented post (with proper attribution) and have the comment deleted.

  • $\begingroup$ I disagree with: "Do not put anything valuable in comments." (At least to some extent.) For example comments like this: "You can find generalization of your problem/very similar problem here (followed by a link to a paper/blog/other question)" are certainly useful for both the OP and other readers of the post. This also helps to populate linked questions list - which might be useful for finding related stuff. But still a comment like this does not actually provide answer, so it cannot be posted as such. $\endgroup$ Oct 26, 2017 at 5:12
  • $\begingroup$ Perhaps this is related to your last paragraph. Possibly, something like this could be added into the text of the question. But I guess you mean mainly edits by the OP when you write: "it would typically be better to incorporate the comment into the commented post (with proper attribution)". $\endgroup$ Oct 26, 2017 at 5:13
  • $\begingroup$ @MartinSleziak Oh yes, information like that is very useful. But it's easiest to find if the note and link is in the relevant part of the post, not as a comment. If you have a remark like that to give, perhaps my recommendation would be to add it to the post (with attribution to yourself, so you don't put words in the OP's mouth) and leave a comment like this: "I added a note and a link about a related result. Feel free to re-edit or rollback!" I agree that "do not put anything valuable in comments" is not universally good advice, but it is an excellent starting point with comments. $\endgroup$ Oct 26, 2017 at 5:22

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