as previously stated, chess.com allows if in online games, but not live games.
there are some on here who still view this as 'cheating'. i believe there is at least one group that plays without any databases, opening trees, or any outside help at all.
This has probably been a hot subject many times on this forum but I wondered what peoples' views were on using the explorer whilst playing? Isn't it cheating??
In all the games I have played on here I have used it only once and then only to confirm that where I was moving was a good move (or at least the best move).