##How do comments work? Comments exist so that users can talk about questions and answers without posting new answers that do not actually answer their parent questions. Comments are often used to ask for clarification on, suggest corrections to and provide meta-information about posts. Comments are intentionally short, having maximum length of 600 characters, and allow only limited markup. URLs in comments automatically become hyperlinks. Each user may post only one comment every 15 seconds. Comments are disposable: unlike posts, there's no revision history, and they can be deleted without warning by their authors, by moderators, and in response to flags. --- ##Who can post comments? All users may leave comments on their own posts and any answers given to their own questions. Users with **at least 50 reputation** may comment on any post. (There is no reputation requirement to post comments on MSO.) See also: http://meta.stackoverflow.com/privileges/comment --- ##Who can edit comments? Users may edit their own comments any number of times for five minutes after they are first posted. Edited comments are marked with a little pencil icon, and a mouseover tooltip over that icon will provide a count of how many times the comment was edited, like this: <sub></sub> Moderators can edit any comment at any time. Moderator comment edits are logged and visible to other moderators, but no revision history is kept. Such edits [will][1] also show the pencil icon. In all other situations, comments cannot be edited. However, in lieu of editing, they may be deleted and resubmitted. --- ##How can I format and link in comments? Comments can be [formatted with a subset of Markdown][2]: **bold** (`**bold**`), *italic* (`_italic_` or `*italic*`), ***bold italic*** (`***bold italic***` or `___bold italic___`) and `code` (<code>\`code\`</code>) are allowed. It is not generally possible to insert line breaks in comments, though some [hacky workarounds](http://meta.stackoverflow.com/questions/3122/formatting-sandbox#comment236011_72773) exist. URLs will be automatically converted into actual links. Links are also allowed by using the Markdown syntax `[link text](http://myurl)`, and there are certain ["magic links"](http://meta.stackoverflow.com/questions/92060/add-data-se-style-magic-links-to-comments/94000#94000) that will be converted to real links automatically. See also: http://meta.stackoverflow.com/editing-help#comment-formatting --- ##Who can delete comments? A user may delete one of his own comments by clicking on the (x) icon that appears to the right of the comment's timestamp when the comment is moused over. A user can delete only one comment every 30 seconds. Moderators can delete any comment, or purge *all* comments from a post. --- ## When should comments be deleted? Generally, there is very little reason to delete existing comments from a question or an answer. There are a few possible scenarios where comments ought to be deleted, but it is worth noting that these should be few and far between, due to their permanent effect on the flow of the comment section. - **Spam:** Unsolicited, indiscriminate promotion of a website or product. - **Noise:** Comments like "[+1 ...][3]" or "[belongs on][4]" can be [flagged for automatic removal][5] without the commenter being punished. Any comment that doesn't contribute to the improvement or understanding of the post itself may be considered noise. Some forms of "noisy" comments are deleted automatically by the system during migration or when a post is closed (see below). - **Thread Cleanup:** Participants or moderators may opt to delete all comments once they've become obsolete: for instance, comments suggesting a change once an edit has been made, flame wars or other off-topic conversation, and comments that have been [moved to chat][6]. A comment should be added by the deleter stating what was deleted and more importantly, *why*. For example: > @all : Comments 1-16 detailing editing discussion were deleted when consensus was reached, to clean up the thread. If a comment doesn't meet either of the criteria above, then it shouldn't be deleted. --- ##What are automatic comments? When someone votes to close a question as an exact duplicate, the system automatically posts a comment to that question under the close voter's name that reads "possible duplicate of -link-" if no such link has already been posted in a comment. <!-- The comment will be upvoted whenever someone else votes to close as exact duplicate with the same question link. <-- Source? I'm pretty sure this isn't true. -Popular Demand --> The comment will be automatically deleted if the question is closed as a duplicate. You still own the comment so you may delete the comment if you desire. This is discouraged as it is helpful to the person who asked the question: if the author thinks their question is unique, seeing a possible duplicate allows them to make changes to differentiate from the duplicate. --- ##How can I link to comments? The timestamp at the end of each comment is a permanent link to that comment. This behavior has existed [since January 2012](http://meta.stackoverflow.com/a/120688/131713). Before then, it was [not officially possible][7] to directly link (permalink) to comments, though an [unsupported workaround][8] existed. [1]: http://meta.stackoverflow.com/questions/66386/can-anyone-at-all-edit-my-comments/66387#66387 [2]: http://blog.stackoverflow.com/2010/01/new-improved-comments-with-reply/ [3]: http://meta.stackoverflow.com/questions/15290/are-all-the-1-comments-really-necessary [4]: http://meta.stackoverflow.com/questions/18494/belongs-on-comments [5]: http://meta.stackoverflow.com/questions/15290/are-all-the-1-comments-really-necessary/15292#15292 [6]: http://meta.stackoverflow.com/questions/133508/comment-chat-migrator-is-a-bit-too-greedy [7]: http://meta.stackoverflow.com/questions/5436/direct-link-to-a-comment/44119#44119 [8]: http://meta.stackoverflow.com/questions/5436/direct-link-to-a-comment/27319#27319