Logic Grid Mysteries

How to play

Each block of the grid crosses one category with another. Tap a cell to cycle it: blank, then a cross meaning those two do not go together, then a tick meaning they do.

Every person has exactly one item from each category, so a tick rules out the rest of its row and its column — and a fact in one block usually settles something in another.

With a keyboard, Tab reaches the grid and the arrow keys move within a block. U undoes, R redoes, C checks and H asks for a hint.

Rules and controls

• Every item belongs to exactly one person, and every person has one item from each category.
• A tick empties the rest of its row and its column.
• Clues come in five kinds: two things go together, two things do not, one person arrived before another, one arrived an exact number of places before another, or one of two possibilities holds.
• The puzzle is finished when one arrangement remains — not when every cell has been filled in.
• Check reports how many marks are wrong, and the count never goes down.
• A hint fills in one cell you could have worked out from what you already have.

Modes

• Guided tutorial — A small mystery that will not let you mark something wrong.
• Mini 3×3 — Three people, three rooms, three keepsakes.
• Standard 4×4 — Four of everything, and four grids to keep straight.
• Expert 5×5 — Five categories. Some of these need a guess and a proof.
• Daily Mystery — One four-by-four a day, the same for everybody.

Tips

• Start with the flattest clues. “X is Y” puts a tick straight in, and every tick clears a row and a column for free.
• Re-read the comparatives after every tick. “Arrived before” says almost nothing on an empty grid and a great deal once one of the two is placed.
• Chase the consequences. If a tick in one block gives you a fact, carry it into the other blocks before looking for a new clue — that is usually where the next two or three answers are hiding.
• An either-or clue is worth marking. It says nothing while both halves are open, but the moment you can rule one out the other becomes a tick.
• On the Expert board, if you genuinely run out of deductions, pick the row with the fewest possibilities left and try one. Some of those puzzles are built to need it.

Privacy and local play

Everything runs in your browser. Your current puzzle, your settings and your best times are kept on this device only, and the button under the grid clears them without touching any other Zerdly tool. No account, no sign-in, and nothing about your play leaves the machine you are on.

Questions

How do I read the grid?

Each block of cells crosses one category with another. A tick means those two go together; a cross means they do not. Putting a tick in a cell rules out the rest of its row and its column, because each person has exactly one of everything — and that is where most of the deductions come from.

Why did marking one cell tell me something about a grid I had not touched?

Because the categories are linked. If Marel carries the lantern, and the lantern is not in the cellar, then Marel is not in the cellar — a fact about a third grid that neither clue mentioned. Chasing those through is most of the puzzle, and it is why the blocks are drawn as one staircase rather than as separate squares.

Does every puzzle have exactly one answer?

Yes, and it is proved rather than assumed. A puzzle is built by drawing the answer first, deriving statements that are true of it, then removing as many as possible while a solver can still find only one solution. If the check runs out of its budget the clue stays rather than being dropped on a guess. Three thousand generated puzzles were verified this way before launch.

What does Check actually tell me?

How many of your marks are wrong, and which cells they are — but not which deduction went astray. That is deliberate: holding a chain of reasoning you are not yet sure of is the activity, and a game that flagged every mistake the moment you made it would do the puzzle for you. The wrong count adds up across a solve and never goes down, so erasing does not tidy the record.

What does the Guided tutorial do differently?

It is the one mode that looks at the answer while you play. A mark that contradicts it is refused rather than accepted, so you cannot build half an hour of work on one wrong crossing-out. That makes it easier, which is why it keeps no best time — a solve that cannot go wrong is not the same result as one that can.

Where do the names come from?

They are assembled from syllables invented for this route, so nothing here is copied from anywhere and none of the people are real. Everything else is a plain noun — rooms, objects, coats, sounds and keepsakes — with no occupations, cities, dates or brands, because a puzzle that asserted something about a real place could be wrong about it.

What do the difficulty labels mean?

They are measured, not attached. A solver records two things about a finished puzzle: how many rounds of pure deduction it yields before it stops giving anything up, and how many times a search had to guess after that. Branching outranks depth, because a puzzle that needs a guess is a different activity from one that does not, however long. The cuts differ by size, from the distributions each size actually produces.

Why is the Mini always about the same difficulty?

Because a three-by-three does not hold enough structure to be hard. Measured over 120 puzzles, two thirds of them land on exactly the same deduction depth. The labels are kept so they mean the same thing everywhere, but the Mini is the introduction and the spread only really opens up at four and five.

How does the daily mystery work?

One four-by-four a day, the same for everybody, built from the UTC date rather than your local one. The puzzle is regenerated from the date rather than stored, which is why the generator version is part of the key. Your results stay on this device.

Is anything sent to a server?

No. The generator, the solver, the hints, the sounds and your progress all run in your browser. There is no account, and clearing this game's data leaves every other Zerdly tool untouched.

Related interactives

• Number Link — join matching numbers without crossing, on a board proved to have one answer.
• Slitherlink — draw a single loop that satisfies every clue.
• Kakuro — a crossword of sums, with one solution and no arithmetic luck.
• Tangram Studio — fit seven pieces into an outline, judged by geometry.