Generally we look for 1–2 pages, but some reviews need to be longer. While we don’t want to overwhelm the author, it’s also important that the author understand your points and rationale. Authors also appreciate it when you refer them to other work in the field that may be useful.
While authors appreciate positive support, it’s important to make sure that your review identifies important limitations, when they exist, in the manuscript. In fact, authors may be confused if you say only positive things in your review, yet recommend rejection to the editor. We hope that your review will be developmental in identifying weaknesses, but constructive in offering authors ideas for how to address these weaknesses as they continue to develop their manuscript.
Reviewers have the ability to make confidential comments that are seen by the editor but not the author. These candid comments can be helpful and we encourage you to use this option when you submit your review.
Other tips for reviewing can be found on our website: Reviewer Resources.