QTZ is an extension of files used by a tool included in the Xcode integrated development environment called Quartz Composer. These are the tools known from macOS. QTZ files store projects made with Quartz Composer. These are most often animations using two-dimensional images, 3D models or audio data. Various types of effects can also be defined in such a project. Some of the QTZ files are screen savers.

Quartz Composer is a visual programming language for rendering graphical data.