Feature or enhancement
--converters prints only the built-in converters and refuses to accept a file name:
$ ./python Tools/clinic/clinic.py --converters Modules/posixmodule.c
clinic.py: error: can't specify --converters and a filename at the same time
But 23 files in the tree define their own converters in [python input] blocks -- path_t, dir_fd, uid_t and others in Modules/posixmodule.c, for example -- and there is no way to get their list and their parameters.
They are registered in the same registry as the built-in ones, so it is only a matter of parsing the given files before printing the list. This is one of the ideas listed in #108643.