neil08 wrote:
Is it allowed for us chess.com users to review an opening or a game before making a move in a game that has already started?
Yes. Check the help page.
"In turn-based chess, you may consult books or databases (including the Chess.com Explorer) for opening moves. "Tablebases," which are specialized databases of particular endgame positions, may NOT be used."
Is it allowed for us chess.com users to review an opening or a game before making a move in a game that has already started?