Four-suit Spider: what the St Andrews solver found, and what we found

Four-suit Spider is the full game: two packs, all four suits, 104 cards across ten columns. Only runs in a single suit move together, and only a complete same-suit run from King to Ace leaves the table. It has a reputation as the hardest of the common patience games, and our own results would seem to confirm it.

Yet the most rigorous study of the game points the other way. Blake and Gent of the University of St Andrews ran 10,000 four-suit deals through a solver that could see every card. It won 9,731 of them outright and did not find a single deal it could prove impossible; the remaining 269 were left unresolved. Their estimate is that 98.487% of deals can be won. Our own no-peeking computer player won 0.2% of 2,000 deals. Both results are right. They measure very different things, and the gap between them is the most interesting fact about this game.

The two results side by side

Put simply: almost every four-suit deal can be won, but it takes information and patience that a straightforward player does not have. solitairex.io places four-suit Spider in its "expert-level" group, with win rates of 11% or less, though it does not say how that range was measured. A skilled human with Undo lands somewhere between our floor and the solver's ceiling; we have no data to say exactly where.

How the four-suit rules work on this site

• Ten columns of six or five cards, last card face up; four columns get six, six get five.
• The 50-card stock is dealt ten cards at a time, one per column, five times. There is no redeal.
• You may place any card on a card one rank higher, in any suit.
• Only a run in one suit can be lifted as a group.
• Any card or run may go into an empty column.
• A King-to-Ace run in one suit is taken off automatically. Eight such runs win the game.
• You get a warning if you try to deal while a column is empty.

Closing the gap between floor and ceiling

Information is the whole game

The solver's advantage is knowing where every card lies. You narrow that gap by uncovering face-down cards as early as possible, and by using Undo to peek down a line and step back. Treat every hidden card as a question you want answered before you commit.

Only build off-suit when you must

A four-suit table fills quickly with mixed runs that cannot move. Each one costs you flexibility. When you have a choice between a same-suit and an off-suit placement, take the same-suit one, even if it looks slower.

Chase an empty column

Our player emptied a column before the first stock deal in only 6 of 2,000 games, and won 2 of those 6. Its only other two wins came without one. The sample is far too small to put a number on, but an empty column was the single most valuable feature in our player's scoring, and it is the space you need to untangle mixed runs.

Think in suits, not in sequences

Our player completed on average 0.05 suits per game. It usually stalled long before finishing any. Aim to complete one suit early, even at the cost of a messy table elsewhere, because each completed suit frees space for everything else.

Accept long games

The four games our player did win averaged about 209 moves. A four-suit win is a marathon.

Play four-suit Spider free

No downloads, no account and no email address: open the page in any modern browser on computer, tablet or phone and the cards are dealt. There are large, readable cards with zoom, Hint, unlimited Undo, Restart, Auto Play, drag and drop or tap to move, and a record of wins, time and moves for the current game. Sound, fullscreen and table colour are all optional.

If four suits is too much for now, two suits or one suit are good places to build up your technique.

Four-suit mistakes to avoid

• Building in whatever suit is available. Every off-suit link is a run that cannot move as one. On four suits, these pile up fast.
• Dealing too early. Each deal buries ten cards. Make every useful move, and use an empty column if you have one, before you deal.
• Spreading effort across every column. Pick one suit and a couple of columns to work on. A single completed suit is worth more than a tidy-looking table.

How we ran the research, step by step

The solitaire-free.uk team ran this study in September 2026. For four-suit Spider we did not build our own solver, so the published St Andrews figure is our reference for how many deals can be won.

1. Rules from our game code. 104 cards in four suits, ten columns, 50-card stock dealt one per column, only same-suit runs move, any card to an empty column, completed runs removed. We assumed that you cannot deal while a column is empty; the site warns, but we did not test exactly what happens.
2. The game in code. We rebuilt Spider in Python with a computer player.
3. Deals kept separate from tuning. The player's scoring was adjusted on seeds 1 to 30 only. Its four-suit results come from 2,000 other deals, seeds 100,001 to 102,000.
4. The player. It searches up to 250 positions ahead using only the cards it can see and never undoes. At four suits it is a very weak player: its result is a floor, not a typical score.
5. Running it. 2,000 deals.
6. The published ceiling. We have no four-suit solver of our own. Blake and Gent's figure of 98.487%, from 10,000 deals with every card visible, is the upper reference.
7. The margin of error. A 95% range shows where the true value very probably lies. With only 4 wins in 2,000 games, our 0.2% has a range of 0.08% to 0.5%.
8. What the numbers can't say. Neither figure is what a typical person wins. The solver sees more than you can; our player does less than you will.

Behind the numbers: the code

We wrote the simulation in Python 3.11 with the standard library only. spider.py covers every suit count, and a shared runner spread the games over 19 worker processes on a 20-core machine; the 2,000 four-suit games took about three and a half minutes. At each turn the player runs a best-first look-ahead of up to 250 positions over the visible cards, scores each by same-suit links, empty columns, uncovered cards and face-down cards remaining, and plays towards the best. Any card it would uncover is treated as unknown, just as it is for you. Ranges use the Wilson score interval.

An AI assistant, Claude made by Anthropic, helped us write and review this code and draft the page. The AI is not the source of any figure: the numbers come from running the simulation or from the published study, and we checked ours against that study before publishing.

Frequently asked questions

Can four-suit Spider really be won 98% of the time?

With perfect knowledge of every card, yes: that is the St Andrews estimate from 10,000 deals. Without that knowledge, it is a very different game.

Why did your computer only win 4 games in 2,000?

It cannot see hidden cards, never undoes, and is a fairly simple player. We report it as a floor so you can see the size of the gap.

Is four-suit Spider the hardest game on this site?

For our computer player, yes. With perfect information it is among the most winnable. How hard it is for you depends on patience and how freely you use Undo.

How long should a game take?

Our player's rare wins took around 209 moves. Expect a long game.

What is a gentler game with the same feel?

One-suit Spider, or Diplomat, another two-pack game. See every game on the games page.

By Admin, solitaire-free.uk. Study date: 18 September 2026.