TFM (for TeX Font Metric) is the standard font description format used by TeX. The TFM library parses and decodes TFM files into an abstract data structure, providing easy access to the corresponding font information in Common Lisp.
In your favorite Lisp REPL, type something like this:
(asdf:load-system :net.didierverna.tfm)
(net.didierverna.tfm:nickname-package)
(defvar *cmr10* (tfm:load-font #p"/path/to/cmr10.tfm"))
You will end up with a font object, containing the decoded font information,
and stored in an easily accessible way. Inspect the object in question to
familiarize yourself with its contents.
TFM comes with both a user manual and a reference manual. Please see the projet's homepage for more information.