Help:Undo

Reverting means undoing or otherwise negating the effects of one or more edits, which results in the page (or a part of it) being restored to a previous version. Partial reversion involves restoring one part of the page to a previous version, but leaving other contributions intact. Self-reversion is the act of reverting your own edits. Reverting does not always use the undo tool. Any method of editing that has the practical effect of returning some or all of the page to a previous version counts as a reversion.

Reverting a contribution may be appropriate. However, reverting good-faith actions of other editors can also be disruptive and may lead to the reverter being temporarily blocked from editing. Read the three-revert rule (part of the Edit warring policy).

Consider carefully before reverting, as it rejects the actions of another editor. In the edit summary or on the talk page, succinctly explain why the change you are reverting was a bad idea or why reverting it is a better idea. In cases of blatant vandalism, uncontroversially disruptive changes or unexplained removals the amount of explanation needed is minimal. But in the event of a content dispute, a convincing politely-worded explanation gains much importance and avoids unnecessary disputes.

There are several ways to revert edits. A reversion can be carried out manually by editing the page to delete wrongly added text or restoring wrongly deleted text. You can do this by copying and pasting text from a past version.

You can also restore a past version of the page. To do this:

It is also possible to undo several consecutive edits, even if they conflict among themselves: view the "diff" to be removed (by selecting the earliest and most recent revisions in the history and clicking "compare selected revisions"), and click the "undo" link.

Administrators and other editors who have been granted access to the rollback feature have additional links that:

Rollback links appear on the user contributions pages, user watchlists, , history pages and diff pages. Note that in the last case, rollback links can be misleading, since reversion is not necessarily to the old version shown (the diff page may show the combined result of edits, including some by other editors or only part of the edits the rollback button would revert). To see the changes the rollback button will revert, view the specific diff that compares the last version from the last editor with the last version from the previous editor.

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Wikipedia