Font-specific metadata locations
SMuFL-compliant applications running on desktop operating systems such as Windows, macOS, or Linux need to be able to determine whether a given font installed on the system is itself SMuFL-compliant.
There is no simple way to encode this information in the font itself15, so instead applications should identify SMuFL-compliant fonts by the presence of the font-specific JSON metadata file in a known location.
System-wide location
It is recommended that, if possible, the font metadata is installed in a system-wide location that allows access by all users on the system:
Windows: %COMMONPROGRAMFILES%/SMuFL/Fonts/fontname/fontname.json
macOS: /Library/Application Support/SMuFL/Fonts/fontname/fontname.json
Linux: $XDG_DATA_DIRS/SMuFL/Fonts/fontname/fontname.json
On Windows, the %COMMONPROGRAMFILES% environment variable expands to C:\Program Files\Common Files, or its localised equivalent.
On Linux, $XDG_DATA_DIRS is an environment variable defined by the XDG Base Directory Specification.
It is typically necessary to require administrator privileges to install files into these locations. However, it is also recommended that, if possible, fonts themselves should also be installed in system-wide locations, so if the metadata is installed by the same installer as the fonts, no additional privileges will typically be required.
User-specific location
If it is impossible or inappropriate to install the font metadata in a system-wide location, use a user-specific location instead:
Windows: %LOCALAPPDATA%/SMuFL/Fonts/fontname/fontname.json
macOS: ~/Library/Application Support/SMuFL/Fonts/fontname/fontname.json
Linux: $XDG_DATA_HOME/SMuFL/Fonts/fontname/fontname.json
On Windows, %LOCALAPPDATA% expands to C:\Users\username\AppData\Local.
On Linux, $XDG_DATA_HOME is an environment variable for user-specific configuration files, defined by the XDG Base Directory Specification.
On macOS, ~ is a shortcut to the current user's home folder, e.g. /Users/username/.
It is not typically necessary to require administrator privileges to install files into these locations. However, files installed in these locations will not be accessible to any other user account on the system.
Private fonts
If a font is not designed to be used outside of a particular, specific application, then of course it is not mandatory for it to be installed in a system-wide location, nor for its metadata to be installed in these publicly accessible locations: a private font intended for use within the confines of a single application may choose to install its metadata in any convenient private location.
Precedence rules
Because font-specific metadata may be installed in either (or both) a user-level location or a system-level location, applications should give metadata found in the user-level location precedence over metadata found in the system-level location.
15. None of the existing tables in TrueType or OpenType fonts lend themselves to storing arbitrary data that could be used to identify a SMuFL-compliant font without subverting the purpose of an existing field in a table, which could have unforeseen side effects. ↩