Go5 contains a 49-card deck in which the cards each have a number, color, and pattern on them. Players start the game with seven cards in hand.
On a turn, a player draws a card from the deck, then places cards down in sets of at least three — with a set consisting of cards with the same number, the same color, or the same pattern — or adds cards to an existing set of theirs. (For the first play, a player must lay down a set of exactly three cards with no jokers. After this, the player is free to play single cards and other sets, using jokers in sets as well.)
You can replace an existing non-joker card in another player's set with one of your cards in hand as long as you use the exchanged card immediately. At the end of your turn, if you have fewer than five cards in hand, you can pick up the top card of the discard pile, then fill your hand to five from the deck.
If a player has a set of five cards, which can contain at most one joker, the player calls "Go5", and the round ends, with everyone scoring points for the cards in front of them and losing points for cards still in hand. If you can use the top card of the discard pile for a "Go5", you can grab the card even if it's not your turn, and the round ends.
Players play a number of rounds until someone passes a predetermined point threshold.