Purpose Recent calls to improve transparency in peer review have prompted examination of many aspects of the peer-review process. Peer-review systems often allow confidential comments to editors that could reduce transparency to authors, yet this option has escaped scrutiny. Our study explores 1) how reviewers use the confidential comments section and 2) alignment between comments to the editor and comments to authors with respect to content and tone. Methods Our dataset included 358 reviews of 168 manuscripts submitted between January 1, 2019 and August 24, 2020 to a health professions education journal with a single blind review process. We first identified reviews containing comments to the editor. Then, for the reviews with comments, we used procedures consistent with conventional and directed qualitative content analysis to develop a coding scheme and code comments for content, tone, and section of the manuscript. For reviews in which the reviewer recommended “reject,” we coded for alignment between reviewers’ comments to the editor and to authors. We report descriptive statistics. Results 49% of reviews contained comments to the editor (n = 176). Most of these comments summarized the reviewers’ impression of the article (85%), which included explicit reference to their recommended decision (44%) and suitability for the journal (10%). The majority of comments addressed argument quality (56%) or research design/methods/data (51%). The tone of comments tended to be critical (40%) or constructive (34%). For the 86 reviews recommending “reject,” the majority of comments to the editor contained content that also appeared in comments to the authors (80%); additional content tended to be irrelevant to the manuscript. Tone frequently aligned (91%). Conclusion Findings indicate variability in how reviewers use the confidential comments to editor section in online peer-review systems, though generally the way they use them suggests integrity and transparency to authors.