Tagging photographs

I finally settled on phraymd. While a little less polished than shotwell, it allows browsing the pictures in a folder and tag them without importing them.

I am accepting Tom's answer anyway, since that would work as well even if with a little more care, and shotwell is already there by default.

I recently did this with a large photo collection, and I recommend you stay with Shotwell for this. You have to use a few tricks to get what you want though.

First, make sure you set 'Write tags, titles and other metadata to photo files' in Shotwell, like in @Paradiesstaub's comment.

If the folder names are to be used for tagging, say like 'New Year's Eve', then import folders individually and tag that batch, they'll be listed as 'Last Import' at the top left of the Shotwell window.

Once you get all your folders imported, tag everyone. Once you have everything tagged, it's already written to the individual files. You can move them around and the tags stay.

At this point, you can leave the files in the original folders, or have Shotwell organise them. I chose to have Shotwell organise them by Year and Month sub-folders. To do this, I selected all the files, and exported them from Shotwell to a backup drive. Then, I deleted everything from Shotwell, and re-imported from the backup drive. Now I just import and tag new ones as I go, and Shotwell watches the directory and keeps it organised.