The use.desc file contains a list of all global non-expanded USE flags, together with a short description. This file should not be modified without discussion on the gentoo-dev list.

The metadata.xml file on each ebuild category contains a list of the local USE flags, together with short description for the package in the said category. More information about the metadata.xml file can be found here.

Having a small number of packages using identically named local USE flags is allowed. If the number starts to grow substantially, it may be worth proposing that the flag becomes a global see .

All non-expand flags must be listed in exactly one of these files.

Expanded flags are listed in desc/${prefix}.desc, where ${prefix} is the name of the environment variable to be expanded in lowercase. Instead of listing the complete flag only the flag's suffix, i.e. the environment variable's possible values are listed.