Queen Place

A six-by-six board, six pieces, and one rule: no two of them may share a row, a column or a diagonal. Three squares are dealt out of play, one piece is already down to start you off, and between them they leave exactly one arrangement that works — proved before the board reaches you by a solver that counts the possibilities and stops as soon as it finds a second one.

The board does the tedious half for you. Every square nothing can go in is crossed out with the reason written under it — col or diag — and the number in front of each row is how many squares that row has left. Those numbers are the whole game: the row with the fewest squares is the row that can go wrong first, so filling it before anything else is never a guess.

It runs entirely on your device: 0 network requests, works offline. No ads, no account, nothing to buy, and no betting, money or prizes of any kind.

1. Focus the board — click it, or press Tab until it is focused.
2. Move the cursor with the arrow keys, or W A S D. It opens on the tightest row on the board, because that is where you should start too.
3. Press Enter or Space on a free square to put a piece there. A square that is out of play or under attack refuses the piece and costs you nothing, so you can never build an arrangement where two pieces attack each other. The only thing you can get wrong is the order you work in.
4. Press the same square again to take that piece back, for free. Pressing a different square in the same row moves that row's piece there instead of adding a second one, because a row never holds more than one.
5. Press Esc to lift every piece you placed and start the reasoning again. That is free and unlimited too. The piece you were dealt stays where it is.
6. Read the number in front of each row: it is how many squares that row has left. A row showing 1 is forced — put its piece there and read the next count. A row showing 0 is stranded, which means something you placed earlier has to move, not that row.
7. Fill all six rows before the placements run out. Only putting a piece down spends one, and spare placements are worth points.

How do you place queens so that none of them attack each other?

Not by trial and error, and not by starting in a corner. Work the most constrained row first. Every piece you place shuts three lines at once — its column and both of its diagonals — so after a couple of placements the rows no longer have six squares each: some have three, some have one. Take whichever row has the fewest squares left and fill it, because that is the row with the least room to be wrong, and filling it narrows every other count for free. Repeat, and a board that looked like a search collapses into a chain of forced moves. That habit has a name in constraint solving — minimum remaining values, or "fail first" — and it is the single most useful thing to know about puzzles of this shape. The one thing to watch for is a row dropping to zero: that means an earlier piece, not the row you are staring at, is in the wrong place.

Is there always exactly one answer?

Yes, and it is proved rather than assumed. A six-by-six board has exactly four arrangements with no two pieces attacking each other. The game draws one of them as the answer first, then deals squares out of play until a counting solver — which walks the arrangements exhaustively and stops the moment it has found two — says only one is left. A square the answer itself uses is never dealt out, so the answer survives by construction, and a square is kept out of play only when blocking it strictly reduces the count. Put any one of the three back and a second arrangement fits, so nothing on the board is spare.

Why three squares out of play, and what is the dealt piece for?

Three, because the four arrangements never put a piece on the same square as one another. Blocking a square therefore rules out at most one of them, so ruling out the three you are not looking for takes exactly three squares — and every one of them is doing real work. It also means the rows start with different counts instead of six each, which is what gives "fill the tightest row first" something to bite on from the very first move. The piece you start with is a foothold rather than a clue, and this page will not pretend otherwise: the out squares already pin the answer on their own, so the dealt piece only saves you the first placement and gives the counts somewhere to fall from.

What happens when the placements run out?

The round ends and the answer is shown, marked on the squares you never reached. The budget is worked out from the board rather than picked: one placement per row you have to fill, plus one spare for every row that offered a real choice when the solver walked the board tightest-row-first, plus three. So a board that falls out by pure counting gives you eight placements for five rows, and a board with three genuine decisions on it gives you eleven. Lifting a piece, moving one and clearing the board are all free and unlimited — the budget is there to stop you sweeping every square, not to stop you thinking.

Is there any money, betting or in-app purchase in this?

None, and there never will be. No currency, nothing to buy, no hints to unlock for a fee, no prizes.

Does it work offline?

Yes. Once the page has loaded once, the whole game — the board, the generator and the solver that proves the answer is the only one — is on your device. No server is involved in play at any point.

Can I play it with a keyboard or a screen reader?

Both. Arrows or W A S D move, Enter or Space places and lifts, Esc clears what you placed. Every square announces what it is in words: free, out of play, shut by a column, shut by a diagonal, your piece. Every row announces how many squares it has left. A dealt piece carries ◆, a piece you placed carries ●, a shut square carries ✕ with col or diag under it, and an out square carries ▨ on a dashed tile — so nothing on this board depends on telling two colours apart.

Six by six, six pieces, three squares out of play and one dealt piece. That board has four non-attacking arrangements in total, so a deal is one of 5 184 combinations: four answers, six ways to block each of the three rivals, and six rows to use as the foothold. Uniqueness is checked exhaustively when the board is dealt rather than estimated, which is exactly what six by six buys — the whole solution set fits in a search that finishes in well under a millisecond, so nothing has to be taken on trust. Boards are rated tight, steady or wide by how many rows offered a real choice on the solver's own route, and the placement budget follows the same number.

Guard Post is the other board puzzle built on the same habit — it asks which squares are still unwatched rather than which rows are still open, and prints the same kind of count. Knight Hop turns on the identical rule under a different name: take the most constrained move, because those are the squares about to become unreachable.

Bookmark this page (Ctrl+D, or ⌘D on Mac) or install the app — it works offline the next time you need it.