402.1. The hand is where a player holds cards that have been drawn. Cards can be put into a player’s hand by other effects as well. At the beginning of the game, each player draws a number of cards equal to that player’s starting hand size, normally seven. (See rule 103, “Starting the Game.”)
402.2. Each player has a maximum hand size, which is normally seven cards. A player may have any number of cards in their hand, but as part of their cleanup step, the player must discard excess cards down to the maximum hand size.
402.3. A player may arrange their hand in any convenient fashion and look at it at any time. A player can’t look at the cards in another player’s hand but may count those cards at any time.