It is not a Wikipedia policy or guideline; rather, its purpose is to explain certain aspects of Wikipedia's norms, customs, technicalities, or practices. It may reflect varying levels of consensus.
This page in a nutshell: A double redirect is a redirect to another redirect. The MediaWiki software is not programmed to follow these redirects. Double redirects are easily fixed by bots, and human editors should devote their efforts elsewhere. However, an editor should not leave behind the double redirects that they created themselves.
A redirect is a special type of page that automatically causes another page to be displayed in its place. A redirect that points to another redirect is called a double redirect. Double redirects are usually created after a page move, when old redirects are left unchanged and pointing towards an old name. These double redirects are unwanted, because Wikipedia's software is currently configured to not follow the second redirect. The MediaWiki feature that would have allowed it was declined as it too hard to implement. If a page is redirected to a redirect, the chain stops after the first redirect, like in this example. These situations create unpleasant experiences for the reader and make the navigational structure of the site confusing.
An example double redirect, having since been corrected by redirecting Morchella esculenta directly to Morchella without using Morel as a half-way point.
Suppose page title A (Morchella esculenta in the example to the right) redirects to B (Morel), in turn redirecting to C (Morchella).
Upon following the link to A, you will see, as illustrated, a page containing:
the page title B;
a large link to C;
a small notice saying "Redirected from A"
Click the "A" in "redirected from A".
You will see a page containing:
the page title A;
a large link to B.
Edit the page by clicking the "Edit" or "Edit source" tab near the top and change B to C.
Double redirects are easily and automatically fixed by bots, and most are fixed within a few days of creation. Because of this, human editors would be best-off putting their time on other tasks that cannot be automated. However, bots cannot fix a double redirect if the redirect page is fully protected. The following bots fix double redirects:
Suppose you want to check whether there are any double redirects to page C. Go to page C and click "What links here" (usually the first link in the "Toolbox" on the left-hand side of the page). Double (or multiple) redirects are those pages appearing in the list with both of these properties:
Indented at least one level in comparison to the page at the top of the list, AND
Labelled "(redirect page)".
Note that if you've just moved page C, then there might be only one page that is not indented, (the page at the top of the list), and everything else might be indented at least one level.
Once all double redirects have been fixed, the "What links here" page will have only three types of pages listed:
Direct links from ordinary pages (not indented, not labelled "(redirect page)").
Direct links from redirect pages (not indented; labelled "(redirect page)").
Indirect links from ordinary pages (indented one level, not labelled "(redirect page)").
