About
Puzzles you can trust.
Most sudoku you find is generated quickly and never checked twice — which is how you end up with a "Hard" puzzle that's secretly ambiguous, or an "Easy" one that's actually a slog. This app takes the opposite approach: nothing reaches your screen until it's been proven, not just produced.
How puzzles are made
Proven, not just generated
Behind every board is a completed grid, dug down one cell at a time — but only while the solver can still prove exactly one solution remains. The moment removing a cell would open a second solution, it stays. That same proof, the solved grid plus the line used to reach it, is what ratings, hints and your end-of-play numbers all draw from.
Both labels are measured, never picked
Every puzzle carries two labels, from one measurement: working the board through with named techniques, in order of difficulty, and taking whichever was toughest. Difficulty collapses that into six familiar tiers, fast to scan before you commit. Logic required states it precisely — the exact technique, linked to its own explainer.
The reasoning has names
The app solves with the same named moves a human would reach for, from Naked Singles up through Triples — which is what powers those ratings, on-demand hints, and an explainer page per technique worked on a real board you pencil in yourself, pulled fresh from real puzzles rather than one fixed example.
How your play is treated
One shared puzzle, every day
One board per calendar day, generated ahead of time through the same proof pipeline as any other puzzle, so it's always ready no matter your timezone. Difficulty cycles through all six tiers on a six-day rotation, and completion counts toward its date even if you finish late — catch up and your calendar still fills in.
Once played, always the same puzzle
A puzzle can't be edited after it's created — not by you, not by an admin. The board you started stays that exact board for as long as it exists, and so does the complete history of every attempt at it.
Built move by move
Every digit placed or cleared is appended to a log in order and never rewritten, so you can resume exactly where you left off, or replay your path afterward move by move. Pencil marks are saved too, but kept out of that log — they're scratch paper, and scratch work never counts as a move or a mistake.
Keyboard and screen readers
The whole board plays without a mouse
Not a grid of click targets with a few shortcuts bolted on afterwards. The board is a real ARIA grid, and every part of a play — reaching it, moving around it, placing digits, pencilling candidates, jumping straight to a cell — has a key behind it.
- One tab stop, not eighty-one
- The cells share a roving tab stop, so one Tab reaches the board and the next moves past it to the digit pad — Tab never walks you through 81 squares to get anywhere.
- You never have to click in first
- An arrow key pressed anywhere on the page, with nothing else focused, walks you onto the grid at its top-left cell. Type into a field or open a dialog and those same keys go straight back to meaning what they mean there.
- Every cell says where it is
- Each one is labelled with its row and column, what it holds, whether it's a fixed clue, and any candidates pencilled into it — so a screen reader reads a place on a board, not a loose digit in a table.
- Changes are spoken, not just shown
- A live region reports what the board alone can't: the notes pad opening, a jump waiting on its next digit, anything that changes while your focus stays put. And a placement made from the keyboard hands focus back to the cell you made it on, so you never lose your place mid-board.
Every key the board listens for
- ↑ ↓ ← →
- Move between cells — W A S D work too
- Home End
- First or last cell in the row; hold Ctrl for the whole board
- Ctrl 1–9 1–9
- Jump straight to a cell — tap Ctrl on its own, then the row digit and the column digit
- 1–9
- Place that digit in the selected cell
- Shift 1–9
- Pencil a candidate, whether or not the notes pad is showing
- 0 Backspace
- Clear the selected cell
- N
- Show or hide the notes pad
- Esc
- Deselect the cell and clear its highlights
The same list sits in the How to play dialog on every puzzle.