Extension:MsCatSelect

The MsCatSelect extension adds a visual interface to the edit page that allows you to:
 * Add a category to a page by selecting the category in a drop-down on the edit page.
 * Remove categories from a page
 * Define a custom list of categories
 * Set a specific sortkey for each category
 * Create a new subcategory in a selected category

Furthermore:
 * If you select a category in the drop-down list another drop-down will be created with all subcategories
 * The selected categories are received through the MediaWiki API
 * User-friendly select boxes with Chosen

$wgMSCS_MainCategories
Is an array filled with categories which should be loaded in the first drop-down. If this array is nonexistent all main categories (categories which are not a subcategory) of the wiki are loaded automatically. Null by default.

$wgMSCS_WarnNoCategories
If you want to get warned when saving a page that has no categories assigned, set  to true in your LocalSettings.php; else set it to false. That is:

$wgMSCS_WarnNoCategoriesException
When  is set to true, you may still want to avoid warnings in certain pages or namespaces. Add those pages and namespaces to the  array to do so. For example: By default the array is empty. You can find all the namespace constants here.

API high limits
By default, the MediaWiki API returns a maximum of 500 subcategories for regular users. If some of your categories have more than 500 subcategories, set the following to overcome this limitation:

Usage
Once the extension is installed and configured, edit a page and scroll to the bottom to see the visual interface for adding or removing categories. Select the categories you want from the dropdown menus and save the changes to add the page to those categories.