About Klondike Solitaire

Klondike Solitaire is the most popular single-player card game in the world. The goal is to build four foundation piles - one per suit - from Ace up to King. Cards on the tableau are arranged in alternating colors and descending rank.

Rules

Tableau: 7 columns; the top card of each column is face-up and available to move. Sequences of face-up cards can be moved as a unit.
Valid tableau moves: a card (or sequence) can be placed on any tableau column if its top card is one rank higher and the opposite color. For example, a black 7 may go on a red 8.
Empty columns: only a King (or King-headed sequence) may be moved to an empty tableau column.
Stock pile: draw from the stock pile (top left) when no tableau moves are available. Cards are dealt face-up to the waste pile.
Foundations: move Aces to the foundations first, then build each suit up in order (A, 2, 3 … K).
Winning: all 52 cards placed onto the four foundation piles.

Strategy tips

Uncover face-down cards first: your priority is flipping the hidden cards in each tableau column. Focus on the columns with the most face-down cards.
Don’t rush to move to foundations: keeping a low card on the tableau lets you build more sequences; sometimes delay foundation moves if a card is needed on the tableau.
Empty columns are powerful: use an empty column to temporarily park a King and rearrange other sequences.

Win odds

The exact winnability of Klondike Solitaire (with draw-1 rules) is estimated at approximately 79–82% of deals being theoretically winnable. In practice, win rates are much lower (around 30–40%) because optimal play is non-trivial. The game was famously included with Windows 3.0 in 1990 to help users learn how to use a mouse.

Solitaire variants

Klondike Draw-3: the stock is dealt three cards at a time, with only the top card of each group playable. This reduces win probability to roughly 1 in 10 deals and is considered a more challenging variant.
FreeCell: all cards are dealt face-up across 8 columns, and four "free cells" hold temporary cards. Because all cards are visible, FreeCell is almost always solvable - only 8 deals in the standard 32,000-deal set are unsolvable. It rewards planning over luck.
Spider (4-suit): builds sequences in all four suits across 10 tableau columns using two decks. The 4-suit version is one of the hardest solitaire variants with a win rate under 0.1% for average players.

Undo strategy

Using undo liberally makes Klondike significantly easier and can increase your effective win rate substantially. If your goal is to improve your understanding of the game, try limiting undos to practice decision-making under uncertainty. For casual play, unlimited undo is a reasonable quality-of-life feature.