View composers are callbacks or classes that Laravel runs when specified views are rendered. They prepare and bind shared view data, such as navigation items, settings, or counts, without making every controller pass the same data manually.

They are commonly registered in a service provider with the View facade. A composer should avoid expensive repeated database work and should be scoped to only the views that need its data. For data that is global to every view, a shared value may be more appropriate, but it should still be kept lightweight.