Everything in rummy reduces to a single question: are these cards a valid group? Get the definitions exactly right and the rest of the game becomes mechanical.
Pure sequence
Three or more consecutive cards of the same suit, using no joker of any kind.
Valid: 4-5-6 of clubs. 9-10-J-Q of hearts. A-2-3 of spades.
The ace is low or high but not both: A-2-3 is valid, Q-K-A is valid, K-A-2 is not.
This is the one group you cannot declare without. Every format requires at least one, and the twenty-one card game requires two. Build it first.
The exception people miss
If the wild joker for the round happens to be, say, the seven of diamonds, then the seven of diamonds is a wild card. But you may still use it as a plain seven of diamonds in a pure sequence of 6-7-8 of diamonds. Used as itself rather than as a substitute, it keeps the sequence pure. Many players do not know this and break up a perfectly good run.
Impure sequence
Three or more consecutive cards of the same suit where a joker stands in for a missing card.
Valid: 5-hearts, joker, 7-hearts — the joker is acting as the six of hearts. Also valid: 9-clubs, 10-clubs, printed joker, where the joker is the jack.
The joker must represent a card that would actually complete the run. A joker cannot be appended to 5-6 of hearts to represent “any card” in an undefined position; it occupies a specific slot.
Sets
Three or four cards of the same rank in different suits.
Valid: queen of hearts, queen of spades, queen of clubs. Also valid with a joker: king of hearts, king of clubs, joker.
Invalid: queen of hearts, queen of hearts, queen of spades. Two decks are in play so you can physically hold two identical cards, but a set may not contain duplicate suits.
A set has a maximum of four cards, since there are only four suits. Adding a joker to an already complete four-card set does not create a five-card group.
Combinations that are not valid groups
- Two cards of anything. The minimum group size is three.
- Consecutive cards in mixed suits — 5-hearts, 6-clubs, 7-spades is nothing.
- Same rank, same suit — covered above.
- A group of jokers alone. Jokers must substitute for something within a real group.
Planning the hand
With thirteen cards you need the whole hand melded, which typically means something like a pure sequence of three, an impure sequence of three or four, and two sets. Count it out when the cards are dealt: how many cards away am I from a pure sequence? If the answer is more than two, that is usually a hand to drop early.
Jokers are worth more in sets than sequences
A joker in a set is replacing one of four possible cards. A joker in an impure sequence is replacing exactly one specific card. Since you cannot use a joker in a pure sequence at all, and sets are the easiest group to complete with one, jokers naturally flow towards sets as a hand develops. Hold them loosely and place them last.
Validity disputes end games and friendships. Learn these six definitions properly and you will never have one.
