Embroidery file formats?

According to this thread (admittedly a few years old, so maybe they've opened up recently) the details of the .art file format is closely guarded by Bernina and not made available to developers, requiring that all work is done through their official design tools.

I would think you could reverse engineer the file format with some trial-and-error modification of the .art file bytes, but the trick is getting those modified files back into the machine. Perhaps a good start would be to modify some bytes and then try to get their design software to re-open the file. The big gotcha with this approach would be if they use a checksum.

You could look at the open source Embroidermodder 2 and it's underlying library, libembroidery. At the time of writing, it doesn't support .ART, but .DST is a common format that most machines support which may work for you. Also, you could use libembroidery's .CSV format to lay out your stitches fairly easily so that all the format specifics are abstracted away and then convert the file with libembroidery-convert to an embroidery format that your machine supports. The .CSV format has the capability of specifying color changes, jump stitches and trimming.

Bernina's .ART format is indeed proprietary, but Berinina owns a software company, OESD, that makes conversion software (e.g. the OESD Magic Box). You can create files using a documented file format, such as .PES, and use their software to convert the PES files into ART.

Here's a resource on the layout of some of the embroidery file formats

disclaimer: the company I work for sells OESD products.