Form melds, reduce deadwood, go gin
Gin Rummy is a two-player game played with a standard 52-card deck. You and the AI are each dealt 10 cards, one card is turned face up to start the discard pile, and the remaining 31 cards form the stock. On every turn you draw one card — either the top of the stock or the top of the discard pile — and then click a card in your hand to discard it. The goal is to organise your hand into melds: sets of three or four cards of the same rank, or runs of three or more consecutive cards in one suit. Aces are low, so A-2-3 is a run but Q-K-A is not.
Any card that is not part of a meld is deadwood. Aces count 1, number cards their face value, and jacks, queens and kings 10 each. The Deadwood box above the table always shows your best possible total, because the game arranges your melds for you, and coloured bars under your cards mark each meld. You may not throw back a card you have just taken from the discard pile. When a discard leaves your deadwood at 10 or less, a Knock button appears; if a discard leaves you with zero deadwood you go gin and the hand ends at once. After a knock the defender lays off unmatched cards on the knocker's melds, and the knocker scores the difference in deadwood. If the defender ends up equal or lower, that is an undercut and the defender scores the difference plus a 25-point bonus. Gin scores 25 plus the opponent's deadwood, with no layoffs allowed. If only two cards are left in the stock and nobody has knocked, the hand is a draw. Each hand is a complete game here: whoever scores wins, and there is no running score to 100.
This is a fast, single-hand version of Gin Rummy with standard knock scoring. You and the AI get ten cards each from a standard deck, you always draw first, and one hand is the whole game. When a discard leaves your deadwood at 10 or less a Knock button appears; at zero you go gin automatically. After a knock the defender lays off unmatched cards on the knocker's melds, the knocker scores the difference in deadwood, and a defender who finishes equal or lower undercuts for the difference plus 25. Gin scores 25 plus the opponent's deadwood with no layoffs. Whoever scores wins the hand, and if the stock gets down to two cards without a knock the hand is a draw. The Deadwood counter works out your best meld arrangement automatically, including long runs and cards that could belong to either a set or a run.
The AI plays only from what a real opponent could know: its own ten cards, the cards that have gone onto the discard pile, and which of those you picked up or passed over. It never looks at your hand or the stock. On Easy and Medium a pickup always means the card finished a meld for it. Hard also weighs every discard by how low its hand is likely to be after the next draw, steers away from throwing cards that sit next to ones you picked up, and will take a low discard when swapping it for a high card clearly beats drawing blind.
Easy takes a discard that completes a meld only about a third of the time, throws a random card about a quarter of the time, and knocks on only about 30% of the turns it could, so many of its hands run down to a draw. Medium always takes a discard that completes a meld, throws whichever card leaves its deadwood lowest, and knocks as soon as it reaches 10 or less. Hard looks one draw ahead when choosing its discard, avoids feeding melds you are visibly building, picks up low cards that cut its count, and knocks at 10 or less until the stock runs low, after which it waits for 8 or less to reduce the risk of being undercut. AI Training has no randomness: it shortlists Hard's five best discards, looks two draws ahead for each against up to 31 possible unseen cards per draw, picks up a discard only when that beats the average blind draw, and knocks as soon as it reaches 10 or less. Single hands of Gin Rummy carry a lot of luck, and over 4,800 test hands it won 2,450 to Hard's 2,347, a small but steady edge. Every level goes gin immediately when it can, and choosing any level starts a fresh game.
For the complete rules, the deeper strategy and the history of the game, read the full Gin Rummy guide, or browse guides for all 33 games.