Hypothes.is is an online annotation tool https://hypothes.is/ AGU has implemented Hypothes.is in GEMS to allow a richer review process. It allows for inline comments and organizes these by reviewers, editors, and authors, and importance. It allows reviews and comments from editors to be easily shared with other reviewers prior to a decision. Authors can respond inline to review comments. We encourage reviewers to use this tool for their review, although it is entirely optional. You can place all your comments in an annotated manuscript, including your summary. If you do this, simply write “see annotated manuscript” in the main box on the review form. However, please provide a qualitative assessment/overview of your impressions of the manuscript either through the annotated manuscript or as a separate review.
Further instructions are here.