GitHub Lines Viewed is a free Chrome extension designed to improve the code review experience on GitHub. This add-on replaces the standard 'files viewed' progress indicator with a more accurate 'lines viewed' metric. This change allows users to get a clearer understanding of their progress through the actual amount of code they have reviewed, rather than just the number of files.

With this simple modification, developers can better manage their time and focus on important changes without feeling misled by the original progress bar. The extension operates seamlessly in the background, requiring no additional setup, thus providing a more informative and efficient experience during code reviews.