Fava can use Beancount's import system to semi-automatically import entries into your Beancount ledger. See Importing External Data in Beancount for more information on how to write importers.
Set the import-config option to point to your import config and set
import-dirs to the directories that contain the files that you want to
import. And if you wish to save new entries elsewhere than main file - use
insert-entry option.
Fava currently only supports entries of type Transaction and Balance. Set
the special metadata key __source__ to display the corresponding text
(CSV-row, XML-fragment, etc.) for the entry in the list of entries to import.
Note that this metadata will be stripped before saving the entry to file.