JabRef is is a program for working with BibTeX and biblatex databases. JabRef program uses no separate internal file format, but directly works with BibTeX and Biblatex. That means, your Bib(La)TeX file is kept as is when opening in JabRef and saving again: You normally load and save your databases directly in the Bib(La)TeX
.bib format. In addition, you can also import and export bibliography libraries in a number of other formats into JabRef.