The USA must publicly share information about harmful and potentially harmful constituents (chemicals) in tobacco products. We sought to understand whether webpages with chemical information are "understandable and not misleading to a lay person."Participants were a national probability sample of US adults and adolescents (=1441, 18% smokers). In an online experiment, we randomly assigned participants to view one of the developed webpages (chemical names only, names with quantity ranges, names with visual risk indicators) or no webpage in phase one (between subjects). Participants completed a survey assessing knowledge, misunderstanding, perceived likelihood, perceived severity of health effects from smoking and quit intentions (smokers only). In phase two (within subjects), participants viewed all three webpage formats and reported webpage perceptions (clarity, usability, usefulness) and perceived impact (affect, elaboration, perceived effectiveness).In phase one, viewing any webpage led to more knowledge of chemicals (48%-54% vs 28% no webpage, s<0.001) and health harms (77% vs 67% no webpage, s<0.001). When exposed to any webpage, 5%-23% endorsed misunderstandings that some cigarettes are safer than others. Webpage format did not affect knowledge or reduce misunderstandings. Viewing any webpage led to higher perceived likelihood of experiencing health effects from smoking (0.001) and, among smokers, greater intentions to quit smoking (=0.04). In phase two, where participants viewed all formats, a visual risk indicator led to the highest perceived impact.Knowledge of chemicals and health effects can increase after viewing a website. Yet, websites may not correct the misunderstanding that some cigarettes are safer.