Mobile won't do it, but the site will

If you want to allow this behaviour you need to disable rules on the settings screen. By default "normal" chess rules apply to the analysis board.

I probably am misunderstanding the question, but normal chess rules should allow a rook to travel from, through, and to squares under attack (i.e., checked squares), just not the king.

it is this game that I was analyzing.  As you can see, as a result of an upcoming trade, the queen will be checking the rook square..

http://www.chess.com/echess/game.html?id=23438329

in the analysis board on my phone, it won't allow me to castle at that point.  in the analyzer on the website, it will..

On what move were you trying to castle?

its too late now, as I've moved on..  This post was really meant as in indicator of the rule problem on chess.com mobile.