Samurai Sudoku FAQ

Samurai Sudoku is a sudoku variant built from five overlapping 9×9 grids: four in the corners and one in the centre. The centre grid shares a 3×3 box with each corner grid, which links all five into a single 21×21 puzzle of 369 cells. You fill every cell so that each row, column, and box of every grid contains the digits 1 to 9 once.

Yes. samuraisudoku.app is completely free and runs entirely in your browser. There is nothing to buy, download, or install, no account, and no video ads between puzzles. Open the page, pick a difficulty, and you are playing.

Sudoku itself grew out of the number-placement puzzle published in Dell magazines in 1979 and was named Sudoku by the Japanese publisher Nikoli in 1984. Samurai Sudoku is one of many larger variants that arrived once sudoku became a newspaper staple; its five-grid shape is a popular way to stretch the same rule into a longer puzzle.

No. Every puzzle is generated on your device when you press Start, so each one is new. A generator builds a full solved shape, removes clues symmetrically, and keeps only removals that leave a single solution at the difficulty you chose.

Treat each of the five grids as a normal sudoku: 1–9 once in every row, column, and 3×3 box. Where two grids overlap, the shared 3×3 box counts for both, so a digit there must fit both grids. Select a cell, enter a digit or a pencil note, and solve outward from cells that have only one possible digit. Fill all 369 cells to win.

The rule is identical; the scale and the links are new. A regular sudoku has 81 cells and one grid. Samurai has 369 cells across five grids, and four shared boxes let information flow between grids. That makes puzzles longer, and it makes progress in one grid unlock cells in another, which many players find more absorbing.

Yes. Each puzzle is generated in your browser and then verified by a solver that counts solutions; any puzzle with more than one is rejected before you see it. That means a purely logical route always exists and you never need to guess.

Levels are graded by the techniques needed, not just clue count. Easy has about 170 givens and can be finished by always filling a cell that has one candidate left. Medium has about 130 givens and needs hidden singles — a digit with only one place in a row, column, or box. Hard has about 100 givens and is the sparsest puzzle the generator can build with a unique solution.

Tap or click a cell, then tap a number or press 1–9. Arrow keys move the selection, Backspace erases, and Shift plus a digit toggles a pencil note. N switches Notes mode, U or Ctrl+Z undoes, H gives a hint, and M mutes sound. Every on-screen button has a label and a visible focus ring.

Notes are small candidate digits you can toggle inside an empty cell to record which numbers are still possible. When you place a real digit, matching notes disappear from every cell it can see, across every grid it belongs to, so your notes never contradict the board.

The four shaded 3×3 blocks are the shared boxes — the overlap between the centre grid and each corner grid. Digits placed there count in two grids at once, so they are the most useful cells to solve first.

Roughly 20–40 minutes for an Easy puzzle, 40–60 for Medium, and an hour or more for Hard, depending on experience. That is longer than a regular sudoku because there are 369 cells to fill. The timer pauses when the tab is hidden, and your puzzle is saved automatically so you can leave and come back.

Start with the shared boxes, where a digit works for two grids, and scan each digit across the whole shape. Fill cells that have a single candidate, then look for hidden singles. Add pencil notes for cells with two or three candidates and let automatic cleanup remove them as you place digits. When one grid stalls, move to a neighbour — its progress often feeds back through the overlap.

Scan the centre grid and the four shaded boxes first. Pick one digit, find every place it is already placed across the shape, and see where its remaining spots are forced. Repeat for the next digit. It is slower than filling the first obvious cell, but it finds the forced moves that unlock everything else.

A red cell repeats a digit that already appears in one of its rows, columns, or boxes. Both cells in the clash turn red, so at least one of them is wrong. Undo to the last placement you were sure about, or erase the more doubtful digit.

Yes. A hint reveals the correct digit for the selected cell (or a random unsolved cell), and a solve that used any hints still counts toward your streak and solved total but does not set a best time.

Yes. Start a puzzle, then press the printer button above the board. The print view shows only the given clues in a clean layout — none of your entries or notes — and you can print to paper or choose “Save as PDF” in your print dialog. See the printable page for a step-by-step guide.

Yes, locally. The puzzle you are working on, your best times, solves, and streaks for each difficulty are saved in your browser, so a refresh resumes exactly where you left off. Nothing is sent to a server and there is no account. A different phone, a new browser profile, or cleared site data looks like a fresh start.

Yes. The board scales to your screen with the number pad and tools directly below it. Five grids fit on a phone in portrait, and a Zoom button doubles the cell size and follows your selection when you want to work with notes. Tablets and landscape phones show the whole board comfortably.

The page needs a connection to load the first time. Puzzle generation and play all run locally in the page afterward, and some browsers keep the tab working without a network, but there is no dedicated offline app or installer.

Open Stats from the icons above the board and choose Reset stats, then confirm with a second tap. That clears best times, solved counts, and streaks for all three levels on this browser. It cannot be undone, and it does not remove the puzzle you are currently playing.

Any current browser with JavaScript: Chrome, Edge, Firefox, and Safari on desktop, plus their mobile versions. If the board does not respond, update the browser, allow scripts for this site, and reload.