Forty Thieves Solitaire: the two-deck game near the top of the ladder

Forty Thieves deals forty cards face up into ten columns of four, puts the other sixty-four in a stock, and then gives you almost no room to work. Cards build down in suit only, move one at a time, and the stock goes through exactly once. There is no second pass to fix a mistake.

Our computer player showed why. Looking a short way ahead and never undoing a move, it won just 5.8% of 3,000 deals and on average got only 34 of the 104 cards home. Please read that figure the right way: it is a floor from a fairly weak player, not the share of deals that can be won. A patient person with Undo and a plan will do better. But it is a clear signal of where Forty Thieves sits on our difficulty ladder: near the top, next to the multi-suit Spiders.

Forty Thieves on the difficulty ladder

The Forty Thieves and Spider players are different programs, so do not read the rows as a precise race. Both are weak, both only see what you see, and both put Forty Thieves and two-suit Spider in the same neighborhood. The solitairex.io site groups Forty Thieves with four-suit Spider in a tier it lists at 11% or less, without saying how that was measured.

How Forty Thieves is played here

• Cards: two standard decks, 104 cards.
• Tableau: ten columns of four cards, all face up.
• Stock: the other 64 cards, turned one at a time onto a waste pile. The top waste card is playable.
• No redeal. You go through the stock once.
• Foundations: eight, two per suit, each built from Ace to King.
• Building: down by one rank in the same suit.
• Moving cards: one card at a time only.
• Empty columns: any card can fill them.

Why it plays like hard Spider

Forty Thieves shares two things with Spider: two decks, and the rule that only same-suit sequences really count. What makes it harsher is the rest. Spider lets a same-suit run move as a block; Forty Thieves moves one card at a time. Spider has no waste to clog up; in Forty Thieves every stock card you cannot place lands on the waste and stays there until something opens up. And there is only one pass. The result is a game where space is everything.

How to steal a win

Bank the visible Aces

More than half of our deals, 57%, opened with at least one Ace ready to play from the tableau. Send it up immediately: a card on a foundation no longer needs room.

Empty a column before you lean on the stock

An empty column is the only extra space you will get, and any card can go into it. Before you start turning stock cards, try to clear the column with the fewest useful cards.

Treat the waste as a second tableau column

Every stock card you turn and cannot play buries the one below it. Before each turn, ask whether the tableau is ready to receive what might come. Turning too early is the most common way to lose.

Expect a long game when it goes well

In the games our player did win, it took about 277 moves, including stock turns. That is the price of moving one card at a time.

Rewind instead of guessing

Because the stock goes through only once, Undo is the only way to see a card and then change your approach. Our player never used it; you should.

The classic Forty Thieves errors

• Building in the wrong suit's column. Only same-suit builds are allowed, so every column quickly becomes "owned" by the suits sitting in it. Before you add a card, make sure you will not need to dig beneath it soon.
• Filling an empty column with one card. Any card can go there, which makes it tempting to use the space for a single stuck card. Often it is better used to shuffle a short same-suit sequence one card at a time.
• Turning the stock to "see what comes". Every card you turn that cannot be played sits on the waste. Turn only when the tableau is ready.
• Racing one foundation. Two piles per suit means you can often afford to wait. Hold cards that are still useful as landing spots.
• Forgetting there is no second pass. Once the stock is gone, the waste cannot be reused. Take the waste cards you need while they are on top.

Tools for a one-pass game

With a single trip through the stock, unlimited Undo is what lets you see a card and still change your plan. Hint, Restart and Auto Play are there as well. The game is free, browser-based on computer, tablet or phone, and asks for no account. Ten columns of two-deck cards fit best in fullscreen, and zoom enlarges them further. Move by dragging or tapping, watch the wins, time and moves counter, and set sound and felt color to taste.

How we tested Forty Thieves, step by step

The spidersolitaire.us team ran this test on September 19, 2026.

1. Traced the rules in our code. Forty Thieves is a variant of our Klondike engine. It deals forty cards face up in ten stacks of four, feeds a 64-card stock to the waste one card at a time with a single pass, builds only within a suit, moves single cards and lets any card into a gap.
2. Rebuilt the game as a program, adapting the player we built for Diplomat to these rules.
3. Dealt 3,000 numbered hands, seeds 1 to 3,000.
4. Chose a floor player. Before every move it weighs up to 300 future positions, but only with cards on view: the stock is a mystery to it, and it never takes a move back. If no line improves things, it flips the next stock card.
5. Played every deal to the end, counting wins, cards home and moves.
6. Looked for published figures. Forty Thieves is not in the main study we check against, Blake and Gent (2026). The only outside figure we have is the solitairex.io tier mentioned above, which gives no method.
7. Worked out the margin of error. The 95% range for 5.8% is 5.0% to 6.7%.
8. Named the limits. This player is weak, so 5.8% is a floor, not how winnable the game is. No all-seeing solver was run for this game.

How the Forty Thieves player thinks

fortythieves.py, a Python 3.11 module with no outside libraries, adapts the look-ahead player we first wrote for Diplomat. Each position it considers gets a score: foundation cards count heavily in its favor, cards resting on lower cards count against it, and same-suit links, empty columns and a short waste pile all help a little. It plays toward the best-scoring position it can find. All 3,000 deals ran on 19 processes in about thirty seconds. Ranges use the Wilson score method. Claude, Anthropic's AI assistant, helped build and review this player and draft the page; the win rate is the player's own result.

Forty Thieves questions

How many cards start on the table?

Forty: ten columns of four, all face up. The other 64 wait in the stock.

Does the stock come round again?

No. On this site the stock goes through once.

Do sequences move together here?

No, only one card at a time.

Is it harder than four-suit Spider?

On our ladder, yes: the Spider player managed 0.2% at four suits, against 5.8% for the Forty Thieves player. Both games sit up near the top rung.

What should I play to practice?

Diplomat is a friendlier two-deck game, and Eight Off trains the same-suit thinking. See the games page for everything else.

By Admin, spidersolitaire.us (Solitairen OOD). Research run September 2026.