How do the comment replies (aka "pinging users") work?
- Who can I send an @reply to?
- How do I respond to a specific user when entering my comment?
- Will they be notified?
- What do people mean when they talk about "pinging" another user?
How do the comment replies (aka "pinging users") work?
You can use @name syntax anywhere in your comment to reply to a specific user. This will notify that user in their global inbox. There can also be notification through email if you set it up in the preferences found in your profile page. This feature is specific to comments and doesn't work in posts.
The author of the specific post (question or answer).
Note that the author of the post will always be notified of any new comment. You may still use it for clarity, if needed; however, if there are no comments, or only you or the author have commented on the post so far, the @name will be automatically removed from the beginning of the comment, as it adds no value. (To avoid breaking sentences, mentions not at the beginning will not be removed.)
Any user who has a visible (non-deleted) comment on the post.
This is usually through the @name feature. Additionally, if a user comments on their own post and there is only one other person who has previously commented on that post, then that person is also notified, even if @name is not used.
However, if the visible comment(s) being replied to are deleted, apart from several exceptions with diamond moderator's comments on deleted posts, then the notification is removed, regardless of whether or not the recipient has already seen the notification.
Any user who has edited the post (does not include pending or rejected edit suggestions).
For questions: The non-moderator user who closed or reopened the question, provided they were the only one to do so. On most sites, this only includes users with gold tag badges who single-handedly closed or reopened duplicate questions. Other cases of this include closures/reopenings on Stack Overflow prior to 2009 and on Hardware Recommendations after mid-2019. If other users were also involved in the closure (e.g., closed by User1, User2, and GoldBadgeUser), no users can be notified.
For questions: the moderator user who closed or reopened the question. Unlike the above case of non-moderator users, there are no restrictions on whether the moderator was the sole user involved in the action. Do note that this checks whether the user cast their binding vote in their capacity as a moderator, so if a user wasn't a moderator at the time but later became one they cannot be notified, and if they were a moderator but later ceased to be one, they can still be notified.
For questions: any user who put a bounty on the question (current or expired)
Keep in mind that the question and answers are all considered independently. For example, if Alice was the author of the question, then you cannot notify her by commenting on Bob's answer (unless Alice also participated in that answer or is following the answer). Similarly, you cannot notify Bob by commenting on Alice's question (unless Bob participated in or is following the question).
Only users who have commented on the post are populated into the list. Editors and other users from the post's history will never appear there, even if they are able to be notified by typing manually. The author is also not included unless they commented.
Users without an account on the site (i.e., if their name shows up without a link, such as deleted users) will not show in the autocomplete, as there's no active account to which to send the notification.
No. Comments containing more than one @name are blocked unless they contain a backtick
In the latter case, only the first name mentioned using the @name syntax will be notified. For example, @alice `@bob Hi!` will notify Alice (if she has participated in that post), but not Bob.
An exception is the case when the first @name either matched nobody or matched the post's author (and thus isn't necessary); in this case, the next @name will be checked. Note that these checks only apply to the first @name, not subsequent ones; if the first one matches someone, and there are multiple @name mentions (or any text of the form
@something), the comment will still be blocked.
When editing a comment within its limited editing period, if you change or add @name, the notification may or may not reach the new recipient depending on timing.
You must include @name, where name is a reasonable match to a user's current display name at the time the comment is submitted. You cannot use previous display names the target may have had.
The notification must begin with a space or be at the start of the comment. For example, you cannot use markup such as italics.
If the first word in the display name is at least three characters long, then there must be a starts-with, case-insensitive match of at least three characters in the display name. This means @a and @ab will never match anyone, unless a user uses a first word that is only two characters. Like: @Jo will notify Jo Miller, but not John, and @B. will notify B. Gates, but not B.Gates. If there are more than three characters in @name, then all given characters must match (neither @alix nor @aliceinwonderland will match user Alice).
Matching is performed in reverse chronological order, so if multiple people named John are participating, @john will match the most recent John. (Use the next rule to differentiate. Note that in this case, the autocomplete may show multiple listings for the same username, but there's no difference in selecting any one of those.)
Spaces are removed from the display names for matching purposes. So to match Peter Smith you may use @pet, @peter, @peters, or @petersmith. The last two are useful if Peter Jones is also participating, who can then be distinguished using @peterj. However, no spaces are allowed in the @name itself. Like to notify P Smith, one must use @psm or @psmith. (Here @P Smith would be handled as just @P, which is too short.) Single quotes, dots, dashes and underscores should not be removed.
The system does attempt to ignore most punctuation to allow for proper notifications, such as a single trailing dot, comma, or colon. The exact matching rules are not documented, but extensive tests performed on 30 August 2011 indicate that the following algorithm is used:
@, where the word boundary is determined by a space, a character not valid in user names (such as
: , / ! ?) or the end of the comment.
. from the resulting string if applicable (and if the string has more than two characters).
's, remove that piece from the string.
Example: The comment ends with
@O'Conner's.). The word immediately following the
. are valid in display names. Then the trailing dot is removed, and finally the
's is removed, resulting in
Some examples of supported notifications:
@name some text
@name: some text
@name. Some text
@name, some text
some text, @name
some text, @name, more text
Some text, @name.
This is mentioned in @name's comment.
@P. for both P. Smith and P. Jones (whoever commented most recently), but not P.Smith nor P.Jones. Likewise,
@P. Smith is handled as
@P., so also matches P. Smith or P. Jones.
@psmith for P Smith
@peterj for Peter Smith or Peter Jones respectively
Examples that will not trigger notifications: