On Stack Overflow, a new user forgot to add the language tag on this post. I asked him about it. After getting the reply, I edited the post to include language tag.

Then I forgot about it for three days and today I went to the post, deleted my own query comment and then moved on to flag the OP's reply as obsolete (since the tag was now added to the post and the brief comment saying "swift....." did not add any value to the post).

To my surprise, as soon as I hit the flag button, the comment was instantly removed and my flag was marked as helpful.

I have never seen obsolete flags getting reviewed so quickly (within 2 seconds, If I am being generous).

How did the comment got deleted so quickly? I can think of only two explanations off the top of my head:

  1. Obsolete flags retain a count like Spam flag. After hitting a total of six flags, the target comment gets automatically deleted.
  2. It was just a coincidence and a moderator just happened to be around to review it within seconds.

Since this is about flagging mechanism which is shared across the network, I thought it would be better to ask this question here instead of Meta Stack Overflow. Do let me know if it is better suited to MSO instead.

  • Of course, but we are talking obsolete flags on comments, right? Commented Mar 27, 2017 at 11:58
  • The comment couldn't have said swift as that is too short. Was it swift..........?
    – rene
    Commented Mar 27, 2017 at 12:00
  • @rene Yes I believe the OP added periods to meet the minimum number of characters/
    – NSNoob
    Commented Mar 27, 2017 at 12:00
  • Huh, isn't it 3 flags for comments?
    – M.A.R.
    Commented Mar 27, 2017 at 12:02

1 Answer 1


When you flag a comment the comment text passes a number of regex rules.

If it matches any of those rules the comment is instantly nuked without going to the moderator queue.

Known patterns are short comments that are extended with dots to meet the minimal length requirement; comments that contain please accept my answer; comments with common swear words (don't be tempted to list those, nor collect them in the comments under this answer).

Not all patterns are public as far as I know and the rules are added/removed/tweaked based on feedback/abuse and false positives. There was an attempt to get this documented in What is the SE version of Seven Dirty Words?

If enough users flag a comment, the comment will be automatically removed once it reaches 3 + (score/3) flags.

The mention of heuristics for comment removal by Jeff Atwood was as early as 2011. And a bit of the inner workings of the blocklists (tags, comments, posts) is explained by Shog9 in the Tavern on the Meta.


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