This paper describes a tool to help instructors guide learners through code examples. The tool captures low-level changes made to a group of files using a popular code editor. Then it allows the programming session to be replayed so that an author can annotate the evolution of the code and explain the reasons behind important decisions. The author-supplied narrative can include text, code highlights, media (hand-drawn pictures, screenshots, videos, and audio files), and self-grading questions. The combination of the narrative and the evolving code are called code ‘playbacks’. Playbacks are viewable in a web browser.

The paper also discusses the experiences of one instructor’s use of the tool in several programming-focused courses over the last two years. The tool provides instructors with an alternative to live coding that allows one to describe code faster with fewer mistakes. In addition, it provides a way for an instructor to build up relevant content that can replace a traditional textbook. The results of several anonymous student surveys are discussed.