[[Category:XYZ]]

A category page can be edited like any other page. However, when it is displayed, the editable part of the page is followed by automatically generated lists of pages belonging to the category, as follows:

The items in the lists all link to the pages concerned; in the case of the images this applies both to the image itself and to the text below it (the name of the image).

For the way in which the lists are ordered, see Sorting category pages below. The first and second lists are divided into sections, according to the first character of the sort key. These initial characters are displayed above the sections. To suppress these, make all sort keys start with a space.

A category page can only display a limited number of items (currently 200). If more pages belong to the category, there will be a link to the next ones.

The categories box for the category page appears at the bottom, in the same place as for other pages. This contains the categories to which the current category page has been added, i.e., its parent categories (the categories of which it is a subcategory). Add a category page to other categories in the normal way, using the "[[Category:Category name]]" or "[[Category:Category name|Sortkey]]" syntax.

A page becomes part of a category if the page's wiki markup contains a declaration for that category. A category declaration takes the form or

[[Category:Category name|Sortkey]]

A category name can be any string that would be a legitimate page title. If the category name begins with a lower-case letter, it will be capitalized. For initial lower-case letters, as in Category:macOS, see the technical restrictions page.

On Wikipedia, it is customary to place category declarations at the end of the wiki markup, but before any stub templates (which themselves transclude categories) and interlanguage links.

When a page has been added to one or more categories, a categories box appears at the bottom of the page (or possibly elsewhere, if a non-default skin is being used). This box contains a list of the categories the page belongs to, in the order in which the category declarations appear in the processed wiki markup. The category names are linked to the corresponding category pages. They appear as red links if the corresponding category page does not exist. If a user has enabled the HotCat gadget, the categories box will also provide links to quickly add, remove, or modify category declarations on the page, without having to edit the whole page.

Hidden categories are not displayed, except as described below under Hiding categories.

To link to a category page without putting the current page in that category, precede the link with a colon: [[:Category:Category name]]. Such a link can be piped like a normal wikilink. (The {{cl}} template, and others listed on its documentation page, may sometimes be helpful.)

Raw information about the members of a category, their sortkeys and timestamps (time when last added to the category) can be obtained from the API, using a query of the form:

Listings of up to 500 members are possible. If there are more members then the results will include text near the end like this: .

This can be added to the previous one, without quotation marks, for the next page of members: ...&cmcontinue=page|NNNN|TITLE

See also: WP:Categorization § Sort keys, and Help:Sorting

By default, a page is sorted under the first character of its name, without the namespace. English Wikipedia groups accented characters together with their unaccented version, so pages starting with À, Á, Ä, will be listed under heading A. Sorting is case-insensitive, so "ABC" comes after "Abacus".

Unlike at Special:Allpages and Special:Prefixindex, a space is treated as a space (coming before all other characters), not as an underscore.

The English Wikipedia has numerical sorting in categories. This means a page whose title begins with a number will be sorted according to the numeric value of the number (even if it is multiple digits). Thus "9 dogs", "25 dogs", and "112 dogs" will all appear under the "0–9" heading in numeric order. If the number includes a comma, space, or period, the sorting algorithm will only consider the part of the number before the separator.

Each of the three lists (subcategories, pages, media files) is arranged in the order explained above (except that, in the subcategories list, the namespace indicator "Category:" is not considered). If an item ought to be positioned within a list on the basis of an alternative name (sort key) for that item, then this can be specified in the category tag that places the item in the list:

For example, to add an article called Albert Einstein to Category:1879 births and have the article sorted by "Einstein, Albert", you would type:

Unlike a piped link (which uses the same syntax), the sort key itself is not displayed to readers. It affects only the order in which pages are listed on the category page.

It is useful to document the system being used for sort keys on the category page. For guidelines about the use of sort keys on Wikipedia, see WP:SORTKEY.

See also: WP:NAMESORT and WP:SORTKEY

It is possible to set a default sort key which is different from {{PAGENAME}} by using the magic word {{DEFAULTSORT}}:

This is often used in biography articles, to make sure the subject is sorted by their last name:

For example, on the Albert Einstein page, {{DEFAULTSORT:Einstein, Albert}} adds the sort key "Einstein, Albert" to all his categories, such as Category:1879 births.

In the case of multiple default sort key tags, the last DEFAULTSORT on the final rendering of a page applies for all categories, regardless of the position of the category tags. This also means that a DEFAULTSORT tag included from a template is not effective if another DEFAULTSORT tag occurs later on the page, even if the later DEFAULTSORT tag is also "hidden" (included by another template). If a category is added inside <ref>...</ref> then DEFAULTSORT may be ignored.

Further information: Help:Searching § Syntax

See also: § Searching for articles in categories, Wikipedia:Category intersection, and Wikimedia bug T3497 "Hierarchical category system is urgently needed"

In addition to browsing through hierarchies of categories, it is possible to use the search tool to find specific articles in specific categories. To search for articles in a specific category, type incategory:"​CategoryName​" in the search box.

A pipe "|" can be added to join the contents of one category with the contents of another. For example, enter

to return all pages that belong to either (or both) of the categories, as here.

Note that using search to find categories will not find articles which have been categorized using templates. This feature also doesn't return pages in subcategories.

Special:Categories provides an alphabetic list of all categories, with the number of members of each; this number does not include the content of the subcategories, but it includes the subcategories themselves, i.e., each counting as one.

The above list contains all categories that have members, regardless of whether they have corresponding category pages. To list all existing category pages (regardless of whether they have members), use Special:AllPages/Category:​.

As described at mw:Help:Magic words,orreturns the number of pages in "Category:Example". Each subcategory counts as one page; pages in subcategories are not counted.

The page Special:CategoryTree enables you to see the tree structure of a category (its subcategories, their subcategories and so on; the display of files and other member pages is optional).

The CategoryTree extension can be used to display such a tree on any page. (This is sometimes done on the category page itself, if the category is split over multiple screens, to make all subcategories available on every screen.) The basic syntax is

<categorytree>​Category name</categorytree>

to display just the subcategory tree, and

<categorytree mode=pages>​Category name</categorytree>

to display member pages as well. They will be indicated by italics.

Dapete's category-visualizer vCat will render charts of the tree structure.

You may also use Template:Category tree or Template:Category tree all, instead.

Warning:

The following code {{PAGESINCATEGORY:{{PAGENAME}}}} will not work as expected when used in the wikitext or in a transcluded template in a category page whose title contains some ASCII punctuations.
For legacy reasons, {{PAGENAME}} may return the page name with these characters being HTML-encoded using numeric character entities : this still works for generating derived wikilinks or displaying page names, or when HTML-encoded this page name is used in a conditional "#switch", but PAGESINCATEGORY does not recognize the category name given in parameter if some characters are HTML-encoded (this is the case notably when the category name contains ASCII apostrophes ' and a few other ASCII punctuations. (The same HTML-encoding is also applied to the values returned by {{FULLPAGENAME}}, {{SUBPAGENAME}}, or {{NAMESPACE}}).
In that case, as the category is not found by its HTML-encoded pagename, PAGESINCATEGORY will unexpectedly return 0 and not its effective number of member pages.
A simple workaround is to transform these HTML-encoded characters back into standard UTF-8-encoded characters, by using the {{titleparts:}} parser function, like this:
{{PAGESINCATEGORY:{{titleparts:{{PAGENAME}}}}}}

Categories can be moved in the same way as an ordinary page; but a certain amount of cleanup may be necessary. A redirect is left at the old category name, and this is not a normal #REDIRECT [[...]] but a

{{category redirect}}

Do not create intercategory redirects other than with a

{{category redirect}}

When the magic word __HIDDENCAT__ is placed on a category page, that category becomes hidden, meaning that it will not be displayed on the pages belonging to that category. On Wikipedia, the magic word is not normally used explicitly, but is applied through the {{hidden category}} template. The feature is mostly used to prevent project maintenance categories from showing up to ordinary readers on article pages.

However, hidden categories are displayed (although listed as hidden):

Hidden categories are automatically added to Category:Hidden categories.

For guidelines on the hiding of categories on Wikipedia, see WP:HIDDENCAT.