How does Debian differ from Debian-Slim?

You can compare the git repos used to build the images (rootfs.manifest is useful). Or you can run each image and see what they show is different:

$ docker run --rm debian:stable dpkg --get-selections >debian-stable-pkgs.txt$ docker run --rm debian:stable-slim dpkg --get-selections >debian-stable-slim-pkgs.txt$ diff debian-stable-pkgs.txt debian-stable-slim-pkgs.txt23,24d22< iproute2                                      install< iputils-ping                                  install35,36d32< libcap2:amd64                                 install< libcap2-bin                                   install40d35< libelf1:amd64                                 install53d47< libmnl0:amd64                                 install77d70< libxtables12:amd64                            install

So by excluding a handful of packages they were able to trim 45MB from the image, or about 40%.

$ docker image ls debianREPOSITORY          TAG                 IMAGE ID            CREATED             SIZEdebian              stable-slim         eb8569e750e6        2 weeks ago         69.2MBdebian              stable              405289501bdf        2 weeks ago         114MB