Convert JPG to NEF

Most likely you have already searched the web for a solution on how to convert a .jpg/.jpeg file to .nef (Nikon Electronic Format RAW Image) format; without any success. That's because it's not possible to convert a .jpg file to an originally generated Nikon Raw image (.nef) with all its metadata (exposure, time, light and so on). Users often look for such a conversion, as they might have accidentally captured images as .jpg instead of .nef files. Once an image is captured/exported as a .jpg/.jpeg file, all metadata is deleted.

Nikon software enables users to save image projects as .nef files, but solely for the purpose of allowing you to work on your .jpg/.jpeg file retaining all previous edits. However, this will not create any additional data. Hence, it is not possible to execute a .jpg/.jpeg to .nef conversion.

You could try use an online conversion tool, such as the Converter365 that appears to be offering such a conversion. We haven't, however, tested the quality of the final files' attributes.

Simply put, it is impossible to convert JPG to NEF directly.
Thus, there is no so-called jpg to nef converter or a free online .jpg to .nef converter to be found.