Help:Diff

A diff is a page or panel showing the difference between two versions of the wikitext of an editable page.

Links to the diffs corresponding to specific edits appear in various lists, including page histories, a user's contributions, Recent changes, Related changes, and watchlists. There may also be links to the diffs between the specified version and the current (last) version. In page histories it is possible to generate a diff between any two versions – select the left radio button for the older version, the right radio button for the newer version, and click "Compare selected versions".

Diffs can also be displayed while editing a page, via the "Show changes" button, to see clearly what changes you are about to make. The diff is also shown during an edit conflict, so you can see exactly what you need to reintegrate.

How it looks
This example shows the top of the diff page (some of the links are dummies). The older version is shown on the left, the newer version on the right. 

Explanation of colours
Unchanged text is black on grey (only parts before and after changed text are shown). Paragraphs which have changed are highlighted in yellow on the old version side, and green on the new version side. Where whole paragraphs have been removed or inserted, the other side is blank (white). Removed text is shown in red on the old version. New text is shown in red on the new version.

Controls and links
The links "Revision as of date" link to each version. If the newer version is the latest one, the link will be to the usual page and the wording will be "Current revision (date)" instead.

The "(edit)" link will take you to the page for editing that version. You may be warned that you are editing an out-of-date revision; if you ignore this and continue, you will revert all the edits made since after that revision.

The "(undo)" link on the newer revision's side will revert that specific edit. When you click the link you can check the diff page of the edit you are going to make, and the edit summary will be automatically filled in with the phrase of MediaWiki:undo-summary. This summary can be edited before you submit your edit. When you are undoing several edits at once, the auto-summary may not work. Though the link exists on all diff pages, it does not function when the revisions conflict. Often versions older than the current one cannot be undone in this way. If it does not work, you will be told that the edit could not be undone and end up in the regular editing page of the current version.

Below that are links to the user page and talk page of the each user who edited the older or the newer versions. Links to the users' contribution lists are also shown. For administrators and rollbackers, a "[rollback]" button also appears where applicable, allowing them to revert all of the edits made by that user.

Then the edit summaries are shown in a parenthesis. If the user has used links in their edit summary, these act as links on the diff page as well. If the editor marked the edit as an minor edit, m appears before the summary.

The "Previous edit" and "Next edit" links lead to earlier or later diffs. When you are viewing the diff between two non-consecutive versions of a page, you will also see the message "(x intermediate revisions not shown.)".

After the table of differences, the latest of the two compared versions is shown fully, unless you have specified in your preferences that this is not to be done.

Linking to a diff
If you need to create a link to a specific diff (for use on a talk page or noticeboard, for example), then locate the diff from the page history, go to the diff page, and copy the URL from your browser's address bar. Then paste this URL (the whole of it, including http:// ) into the text of the page where you want the link to appear, putting single square brackets [...] around it.

Another way of creating links to diffs is described at Template:Diff.

The URL for a diff is based on the  value of the old revision. If a revision has oldid value 12345678, so its URL is:



then URLs for its diffs may take the forms:


 * diff with the current version:
 * diff with the previous version:
 * diff with version 10000001:

Deleted revisions
An administrator can see deleted revisions and diffs but those diffs can only be shared with other administrators. In order to allow all users to view the diff, the revisions in question need to be restored temporarily.

Miscellaneous
When moving or copying a piece of text within a page or from another page, and also making other edits, it is useful to separate these edits. This way the diff function can be usefully applied for checking these other edits.

The diff shows differences per line. Some editors find that adding manual line breaks improves the diff function.

If you trying to find the point in a page's history where a particular change was made, and searching the edit summaries does not help, try taking the diff between points roughly 1/3 and 2/3 of the way through the history. From this diff, you can work out in which of the three parts of the history the change occurred. Repeat this process, narrowing the "search space" by a factor of three each time, until the precise edit where the change was made is identified. You can also use the external WikiBlame tool, which automates this searching process.

In the case of the Classic skin with quickbar, the diff page does not have the quickbar, to provide more space. Therefore the diff page is also useful for viewing the page on full screen width, without changing the preferences. With the Monobook skin the panels on the left are also on the diff page.

On a diff page sometimes the display may be wider than the screen, because there are two columns, but also because URLs (especially long ones) are not hidden. In such cases, you must then use the horizontal scrollbar of the browser to see all the display.