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. We also encourage authors to respond to reviewer comments directly in hypothes.is to alleviate the need for a response to reviewer file. Again this is also optional, and authors may still submit a response to reviewer file, either alone or in conjunction with responses in hypothes.is.
Further instructions are here.