Very short text strings
Snackbars should generally only be tall enough to accommodate one string, and the string should be directly related to the operation performed. They cannot contain icons or action icons. Actions are in the form of text.
Transient
For usability, snackbars should not contain the only way to access a core use case. They should not be persistent and stack, as they are above other elements on screen.
0-1 actions, not dismiss or cancel
If an action is present, comply with dialog spacing and affordance rules. For two or more actions, use a dialog, not a snackbar, even when one of the actions is a dismiss action. If the action(s) described in the snackbar are important enough to block usage of the screen, it should be a dialog.
Don’t block the floating action button
Move your floating action button vertically to accommodate the snackbar height.
