Wikipedia:Categorization dos and don'ts

This is an information page.

It is not an encyclopedic article, nor one of Wikipedia's policies or guidelines; rather, its purpose is to explain certain aspects of Wikipedia:Categorization. It may reflect differing levels of consensus and vetting.

Categories are a vital tool for navigating Wikipedia.

When categorizing pages:

DO:
Use the most specific categories possible.
Categorize based on defining characteristics.
Add pages to multiple categories in overlapping trees.
Provide sort keys or a {{DEFAULTSORT:}} key.
Add cleanup templates where needed.

DON'T:
Don't add pages to non-existent categories.
Don't categorize based on trivial characteristics.
Don't add pages to non-neutral or unverifiable categories.
Don't categorize fictional subjects together with real ones.
Don't apply maintenance categories directly: use templates.