Introduction. The article explores whether members of a Facebook group view the group as a source of credible information and how they evaluate the credibility of information provided in the group. Method. The data for this study were collected using semi-structured interviews with 19 members of a closed Facebook group for mothers. Analysis. The constant comparison technique was used to analyse the interview transcripts which were interpreted from a sociocultural perspective using the concepts of cultural tools and cognitive authority. Results. The findings show that although the participants used the Facebook group to seek information, they did not consider it a credible source of information. The study contributes the insight that assessments depended on the domain of the information and that participants distinguished between information offered in a professional or a personal capacity. A number of cultural tools were employed to negotiate credibility assessments, including language use and writing style, expertise, life experience, educational background, and similar lifestyles, parenting values and worldviews. Conclusions. The Facebook group was characterised by a combination of familiar and unfamiliar others, of the sharing and seeking of information from different domains and of first- and second-hand knowledge. The participants employed various cultural tools to assess credibility in this mixture of knowledge domains and information sources.