We can define build-packages globally in the snapcraft.yaml. This means that the build-packages are not for a part in particular, but for all of them. With build-snaps we can't define them globally. We can only define them inside a part. To reproduce, try to build the following yaml: name: build-package version: '0.1' summary: install a build-package description: Install a build-package. build-snaps: ['hello'] parts: hello: plugin: nil