Background: This paper outlines the findings of a sociocultural study that examined how digital contexts shape historical thinking. It was assumed that the tools used to engage with historical information mediate thinking, and that when evaluating historical information online, participants would draw upon heuristics associated with Historical Thinking (Wineburg, 1991) and website evaluation. Method: The study involved qualitative interviews with historians and university students who evaluated three historical websites using a think-aloud protocol followed by semi-structured questioning. Findings: While sourcing, corroboration and contextualization remain the basis of disciplinary inquiry, the specific nature of each heuristic shifted when being used to evaluate online material, and a new category of intertextual 'hybrid' heuristics was formed as participants adapted general digital heuristics to evaluate historical information. Furthermore, these 'hybrid heuristics' had divergent effects on participants: for the students it appeared to inhibit critical historical thinking, whereas for the historians it formed the basis of their deep critical appraisal. Contribution: The findings have implications for research on historical thinking, history education and critical website evaluation.