  Users are increasingly being warned to check AI-generated content for
correctness. Still, as LLMs (and other generative models) generate more complex
output, such as summaries, tables, or code, it becomes harder for the user to
audit or evaluate the output for quality or correctness. Hence, we are seeing
the emergence of tool-assisted experiences to help the user double-check a
piece of AI-generated content. We refer to these as co-audit tools. Co-audit
tools complement prompt engineering techniques: one helps the user construct
the input prompt, while the other helps them check the output response. As a
specific example, this paper describes recent research on co-audit tools for
spreadsheet computations powered by generative models. We explain why co-audit
experiences are essential for any application of generative AI where quality is
important and errors are consequential (as is common in spreadsheet
computations). We propose a preliminary list of principles for co-audit, and
outline research challenges.
