I had a chuckle when I looked at the source code and could not find a Dockerfile in there. I want to kick the tires on it and the easiest way would be to run it as a Docker container against an existing file and alas, I cannot.
Regarding this part, you can always just run a base image and add the app yourself. I'm on mobile so can't test, but should be along these lines:
docker run --rm --name dockerfmt \
-v /path/to/Dockerfile:/tmp/Dockerfile \
golang:1.24-alpine sh -c \
"apk add git && go run github.com/reteps/dockerfmt@latest /tmp/Dockerfile"
For this part yes, you'd still need one, but it can be any of your own.
so you can still have no dockerfile and the irony is not ruined