Writing a commentary about a paper from a collaborator -- is it research misconduct? I want to write a commentary (for a journal) about a paper a collaborator has published.
Is there a conflict of interest? Is it research misconduct if I write the commentary?
If you want to be &quot;safe&quot; just reveal the relationship. Then people can better judge whether what you have to say is just fluffing (if it is too positive) or grumpiness/sabotage (if it is too negative) or that it is a fair assessment of the other work as it should be.

For an explicit answer to the topline question, however, motive matters. It is possibly misconduct either to try to &quot;catapult&quot; the work of a collaborator or to sabotage it. Writing a fair analysis isn't misconduct.

Following up on a comment, if the editor thinks that writing such commentaries is a clear conflict, then you shouldn't bother to submit it. In such a case, publishing it without disclosing the relationship would be misconduct, not because of the writing of the commentary, but from the deceit of withholding information from the editor.