The page before they started basically told them everything we'd do. My line of thought was that anyone being able to bypass it is worth interviewing anyways.
I explicitiy told them that we'd log EVERYTHING and asked them to directly write the browser in the JS IDE (well, syntax highlight but no autocomplete) that'll come up, and that they shouldn't switch tabs or windows.
I still think this is fair, for litterally fizzbuzz, nothing similar or anything, just fizzbuzz.
I didn't care about (small) syntax/logic errors or anything (because you'd never run the code), but you wouldn't believe the amount of people unaware of the modulo operator.
It's really just fizzbuzz, not an approximation of real life world, we had on site interviews for that (Switzerland is quite small, not sure how that'd apply to the US).