Metadata for SMuFL-compliant fonts
To help software developers integrate SMuFL-compliant fonts, it is recommended that font designers provide a font-specific metadata file, in JSON format, in the distribution package for their fonts.
The metadata file allows the designer to provide information that cannot easily (or in some cases at all) be encoded within or retrieved from the font software itself, including recommendations for how to draw the elements of music notation not provided directly by the font itself (such as staff lines, barlines, hairpins, etc.) in a manner complementary to the design of the font, and important glyph-specific metrics, such as the precise coordinates at which a stem should connect to a notehead.
Glyph names may be supplied either using their Unicode code point or their canonical glyph name (as defined in the glyphnames.json file – see above). Measurements are specified in staff spaces, using floating point numbers to any desired level of precision.
The following key/value pairs are mandatory:
| Key name | Description |
|---|---|
| "fontName" | The name of the font to which the metadata applies |
| "fontVersion" | The version number of the font to which the metadata applies |
All other key/value pairs are optional.
The following key/value pairs may be used, if desired, to specify the useful range of sizes for which the font is designed:
| Key name | Description |
|---|---|
| "designSize" | The point size for which the font is optimized, specified in integral decipoints (1/720th inch) |
| "sizeRange" | An array of two point size values, describing the smallest and largest point sizes for which the font can serve well, specified in integral decipoints (1/720th inch) |
These values are based on features in the OpenType font specification to specify design size and size range; initially these were encoded in the size feature in the GPOS table, but has been superseded by the STAT table, which defines sizes for families with optical size variants.