MediaWiki allows you to categorize pages and files by appending one or more Category tags to the content text. Adding these tags creates links at the bottom of the page that take you to the list of all pages in that category, which makes it easy to browse related articles. It also helps for those interested in the topic, to quickly find what it is related to.
Categorizing in a Nutshell
Add a page to a category
To add a page or uploaded file to a category, simply edit the page and add the following text (where NAME is the name of the category you want to add it to).
Any number of Category tags may be added to the page and the page will be listed in all of them. Category tags can be added wherever you like in the editing text, but they are usually added at the very bottom for the convenience of other editors.
Adding Category tags to categories will make them subcategories. It is a good idea to organize all your categories into a hierarchy with a single top level category.
Spaces and line breaks before categories are ignored, thus
* A list item [[Category:Some category]] Some text
will be rendered the same as
* A list item Some text
You will need to manually add a <br /> tag or a line break after the category.
A sort key specifies where the page will appear in the category list, and under which letter heading. (By default, the page is sorted under the first letter of its full name including its namespace.) You can add a sort key to a page by adding it inside the Category tag. For example, the tag below will add the page under the heading "S".
Sort keys are case-sensitive, and a space is also valid. The order of the sections within a category follows the Unicode sort order. The sort key does not change the page title displayed in the category.
Create a category
A category can be created the same way as other wiki pages (See Help:Starting a New Page); just add "
Category:" before the page title. (Category lists exist even if their description page is not created, but these categories are isolated from others and serve little purpose for organization or navigation.)
It is not possible to rename (move) a category, unlike other wiki pages. It is necessary to create a new category and change the Category tag on every page. The new category will not have the older category's page history, which is undesirable if there are many revisions.
To avoid extra work, try searching within your wiki before creating a new category. The list of all categories can be found in "Special pages" in the "tools" box of the sidebar.
The categories that a page is in are normally listed at the bottom of the page. A category can be hidden from these lists by adding "
__HIDDENCAT__" magic word to the category page. (Each user can choose to see them in a separate "Hidden categories" list, by checking "Show hidden categories" in the "Appearance" section of Special:Preferences.)
Hidden categories are not hidden on category pages (bug 15550).
Linking to a category
To create a link to a category, use a leading colon before the category name. (Without this colon, it will add the current page to the category.) To change the link text, write the text inside the link tag after a pipe.
For example, to link to "Category:Help", write "
[[:Category:Help]]", which will result in Category:Help.
Redirect pages (to categories) must also use the colon, otherwise it will be added to the category as well as redirecting.