# When writing a comment, how do I ensure that the person it is addressed to gets notified?

Often I want to address a comment to a specific user. How can I do that? I've seen that I've got to use the @ symbol for this, but I didn't find the exact rules in the faq. Can I notify any user? Do I have to put the full user name after the "@"? And what happens if the name contains a space?

Just as an example, if I want to notify TH., should I use "@TH" or "@TH."?

• I have heard somewhere that you need at least 3 characters after @ to get a notification. That is, something like @TH isn't enough but @Hendrik is. – Jukka Suomela Oct 27 '10 at 12:05
• @Jukka: I'm not sure. Here I think I did not get a notification when "@Hendrik-vogt" was used. (Did you get a notification for this comment of mine that just used "@Jukka"?) – Hendrik Vogt Oct 27 '10 at 12:11
• Yes, I got a notification. Of course if the part after @ does not match the beginning of your user name, you won't get a notification. @foobar won't notify the user "foozap", and @Hendrik-vogt won't notify the user "Hendrik Vogt". However, @Hendrik or something like @Hen should notify you. – Jukka Suomela Oct 27 '10 at 12:25
• Jukka's explanation sounds very convincing. (Thanks a lot!) Still, my questions remain unanswered. – Hendrik Vogt Oct 27 '10 at 12:28
• Ah ha. Looks like I was wrong. I guess that TH is just too short. =) – TH. Oct 27 '10 at 14:35
• @TH.: Do you get notified by this comment? After reading your comment mentioned in the question, I now always write "@TH." instead of "@TH". – Hendrik Vogt Oct 27 '10 at 14:42
• @Hendrik: Yeah, I did. – TH. Oct 28 '10 at 5:48
• @TH: Yet another test: Do you get notified by this comment? (If you're surprised, have a look here.) – Hendrik Vogt Jan 24 '11 at 13:47
• @Hendrik: Yep! That's great. I'm sure I'll miss many fewer comments. – TH. Jan 24 '11 at 16:31
• @TH: Amazing! This is not really described at the above link, and neither here nor here. Or do you find it there? – Hendrik Vogt Jan 24 '11 at 16:34
• @Hendrik: Nope. My best guess is that after the H in TH. counts as a word boundary. I think it does in perl. perl -e '"TH." =~ /(.*)\b(.*)/; print "[$1][$2]\n"' prints [TH][.]. – TH. Jan 24 '11 at 16:47
• @TH: Thanks for the explanation. I've updated the answer and cleaned up the question. Hope you don't mind that I abused you as an example case. – Hendrik Vogt Jan 26 '11 at 8:44

The shorter, incomplete, but easier-to-digest-first rules as described by Jeff Atwood, but with an update due to changed behaviour:

1. Only applies to other people in the comments that you are commenting on.
2. Response must include @username that you are referring to, where "username" is a reasonable match to the user's current display name (as seen in the comments above yours).
3. There must be a starts-with, case insensitive match of at least THREE characters to the displayname. UPDATE: @ab will only give a match if the third letter of the displayname is a non-letter.
4. Spaces cannot be used to match, so if the person's display name is "Peter Smith" then just use @peter to match.
5. Matching is performed in reverse chronological order, so if there are five people named "John" in the comments, writing "hey @john, have you considered apples?" will match the most recent John to comment.

These older rules don't include some later features: now the look up for names tries to look in more places for a match and tolerates omitted spaces. And: anyone who edits a question or answer is also on the list of people who are considered possible matches for notification. Hence, the official rules, as described on meta.SO:

1. Notifications apply to the author, commenters, and editors of the question or answer that you are commenting on—users not in that list cannot be notified. The question and answers are all considered independently. For example, if Alice was the author of, commented on, or edited the question or her answer, then you cannot notify her by commenting on Bob's answer (unless Alice also participated in that answer), and vice versa.

2. You must include @name, where name is a reasonable match to a user's current display name. Users who have not set a display name in their profile are not notified.

3. 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).

4. Matching is performed in reverse chronological order, so if five people named John are participating, @john will match the most recent John. (Use the next rule to differentiate.)

5. 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. Single quotes, dots, dashes and underscores should not be removed.

6. Special characters are replaced with their simple equivalent. To reply to Piëre you can use both @piëre and @piere. And to reply to Jörg you could use @jorg, but not @joerg.

7. 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.

8. 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.

9. 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.

10. The first author of the question or answer will always be notified of any new comment. There is no need to use @name to notify them. (You may still use it for clarity, if needed; however if only you and the author have been commenting on the post so far, the @name will be automatically removed from the beginning of the comment, as it adds no value.)

11. The notification must begin with a space or be at the start of the comment. For example, you cannot use markup such as italics.

12. Single trailing punctuation such as a dot, comma or colon is ignored. Like @name, yes works, but @name... no does not. (Though a dot is valid in a username, the last dot is removed for matching. Adding excessive dots is not supported.)

13. The notification only works for the username that is current at the time the comment is submitted, not any previous username(s) the target may have had.

• @name some text
• @name: some text
• @name. Some text
• @name, some text
• some text, @name
• some text, @name, more text
• Some text, @name.

Examples that will not trigger notifications:

• @name...
• abc@name
• *@name*
• *@name:*
• [@name](http://some-url)
• @[name](http://some-url)`
• Great link, thanks. A more complete explanation can be found here – Hendrik Vogt Oct 27 '10 at 13:02
• Could you please add to your answer that spaces can now be omitted to get a match, so e.g. "@petersmith" will work? – Hendrik Vogt Oct 27 '10 at 16:22
• @Hendrik: Thanks, I'd completely forgotten that the rules for comments had changed. I've pasted in Roger Pate's post. – Charles Stewart Oct 27 '10 at 18:38

With regard to the FAQ bit, I suspect that we've sort of lost a bit of steam there. It may partly be to do with the fact that we can (at the moment) only edit the first part of the FAQ so suggestions on what goes in the rest is a bit like arguing over what colour the deckchairs should be on the iceberg.

• OK, that explains the loss of steam that I have noticed, too. Thanks! – Hendrik Vogt Nov 3 '10 at 9:50
• @Andrew: Maybe this question should also be "faq"? – Hendrik Vogt Jan 26 '11 at 7:35
• @Hendrik: I agree (and done), though I think that the question text should be cleaned up a little to make it easier for a new user to get the information fast. – Loop Space Jan 26 '11 at 8:16
• @Andrew: Yes, of course. I'll do that right now; just wanted your feedback first. – Hendrik Vogt Jan 26 '11 at 8:19
• @Hendrik: Great. By the way, I think that what you're doing here - figuring out which "questions" should be in the FAQ category is really good. Do you know about the "featured" tag? It's another moderator-only tag and it means that the post gets listed in the "On Meta" (or whatever it's called) list on the main site. If you come across a post here that should be there, please let me (or another mod) know. Maybe even a "meta meta question" that contains links to other useful questions here. – Loop Space Jan 26 '11 at 8:23
• @Andrew: Yes, I do know about the "featured" tag, and I do have a candidate. That one would have to be updated, too: For example, a link to this very question and to my new post about inline code would be nice. And some of the existing links there are less relevant than others; maybe one could make that two sections. What do you think? – Hendrik Vogt Jan 26 '11 at 8:28
• @Hendrik: I think that that would be a good template, but that it should be rewritten from the point of view of being useful to a new user; so effectively saying that since we can't edit the FAQ, here's our unofficial FAQ, but using that question as a guide to what should be in it. – Loop Space Jan 26 '11 at 8:31
• @Andrew: Agreed. Are you willing to make a start? – Hendrik Vogt Jan 26 '11 at 8:32
• @Hendrik: I'll have a go. – Loop Space Jan 26 '11 at 9:09
• @Hendrik: Aakk, have to be tomorrow now. – Loop Space Jan 26 '11 at 21:11
• @Andrew: I've added the two links and did some reordering according to relevance (of course entirely subjectively). It's still far from good; maybe you have an idea how to make it more accessible. – Hendrik Vogt Feb 13 '11 at 9:14

From meta.SO, Micro-refinement to notifications for comments of others posts: If a user comments on their own post and there is only one person who has previously commented, then that person gets notified when the post author comments even if '@user' is not specified.

This was implemented on 9 March 2011. It is particularly helpful for new users trying to give feedback.