What can cause a question to be "bumped" to the first page in the Active tab of a Stack Exchange site? (Changing the "Last Active" date.)
The following activities will cause a question to be bumped:
- Addition of an answer
- Editing the question or any of its answers (even if the answer is deleted) (with some exceptions; see Exceptions for edits bumping posts below)
- A suggested edit gets approved
- Using the rollback button or the 10k+ inline tag editor does count
- Editing duplicates list of the question
- Starting a new bounty (not awarding of an existing bounty, see below)
- Successful reopening (if the question was closed previously)
- The Community user will bump non-negatively scored, open questions every hour that have at least one answer scoring 0 and none scoring more than that.
- Questions are picked randomly from the top-viewed questions with last activity more than 30 days ago.
- Once a question is bumped, it will be ineligible for bumping for the next 120 days, unless it receives new activity after the last bump. (Bumping a question counts as new activity, so at a given time, questions bumped within the last 30 days are guaranteed not to be bumped.)
- The maximum number of unanswered questions bumped per hour depends on the site: 4 per hour on Stack Overflow, 2 per hour on Super User, and 1 per hour on Meta Stack Exchange and all other sites.
- Some sites prevent additional questions from being auto-bumped while an auto-bumped question is near the top of the front page (i.e. the most recently active posts). If one of the top N posts, sorted by activity date, has been bumped, no questions will be auto-bumped by the Community user that hour.
The following activities will not cause a question to be bumped:
- Edits to a question or any of its answers that fall under the Exceptions for edits bumping posts below
- Deletion or undeletion of the question or an answer
- Upvotes/downvotes on the question, answers, or comments
- Creation, modification or removal of comments on the question or an answer
- Casting/retracting close and reopen votes on the question
- Successfully closing the question
- Awarding a bounty to one of the question's answers
- Flags (offensive/spam/moderator)
- Pending edit suggestions
- Accepting an answer
- Protecting or unprotecting the question
If bumping on the home page ever causes you to miss new answers on a site consider bookmarking links like this one to New answers on Meta Stack Exchange.
Exceptions for edits bumping posts
Under some specific cases, edits to a question or any of its answers will not result in the post being bumped:
Only edits that generate a new revision in the edit history will ever result in the post being bumped. Edits on a post within the 5-minute grace period fold the changes back into the previous revision, and will never cause the post to be bumped.
Questions with sufficiently low score will not show on the homepage when either they or their answers are edited, though they will still be shown on the Questions page. The "sufficiently low" threshold is -4 on main sites and -8 on meta sites (as of Aug 25, '10 -- see Grace Note's comment).
Edits made by the Community user as part of an automated script will not bump the question. For example, globally changing certain
https, or removing the featured tag after 30 days. This doesn't apply to all Community user edits; anonymous edits (of which Community takes credit) will still bump posts.
Historically-locked questions are not bumped when they or their answers are edited by moderators.