The poster explores documentary practices in web environments where credibility is constructed and agreed upon. Based on studies of open peer review processes in scholarly journals and of discussions of credibility in comments to a climate change blog, four dimensions of credibility assessment activities are identified: gatekeepers/open participation; formal credibility assessment/intrinsic plausibility; individual credibility assessment/collective credibility assessment; and experts/laymen. Within each dimension, various positions and tensions with regard to credibility are exemplified. It is concluded that whether or not participation in credibility assessments, or review, becomes a collective activity within a documentary practice depends on the interaction between the affordances of the inscription technologies, social affordances and institutional practices.