We explain the rules for posting on PubPeer and offer some advice on writing effective comments.
By far the most important rule for commenting is to base all of your statements on *publicly verifiable* information. This will usually be the data published in the paper you are commenting on, but could also be another paper or some other source such as a book, newspaper or web site. Please cite your sources to allow easy verification.
Observation of this rule automatically focuses discussion on the facts and the science. It also greatly reduces the legal risks to PubPeer and to you. If comments only involve immediately verifiable facts there should be no difficulty in proving the truth of the statements. The truth is of course a strong defence in any defamation/libel case. However, our aim is not just to have a strong defence, but never to need one. If your comment only contains the obvious truth, that should discourage unhappy authors from initiating any legal attack.
Concentrating on the published facts means avoiding any speculation about the intentions or actions of authors. Although it is almost inconceivable that some of the anomolies highlighted on PubPeer arose in any innocent manner, accusations of fraud, misconduct, deceit or incompetence are nevertheless forbidden on PubPeer. In any case, a clear factual argument is usually all that is required to allow readers to draw their own conclusions, as you will observe as you read the comments. See also https://pubpeer.com/misconduct .
Be polite; this should follow fairly automatically from being factual.
Although it is important to be concise, a minimum of context and explanation are very helpful to readers, so please consider providing these even if that does require extra work.
Please also proof-read your comment carefully before posting it. Registered users can edit or even delete posts until somebody else replies, but comments made via the unregistered route obviously cannot be altered once submitted.