How to play Sudoku
Give every digit its place in a 9 × 9 grid. Fixed clues stay in place while you fill the empty cells and keep track of possibilities with pencil notes.
- Put the numbers 1–9 exactly once in each row, column and 3 × 3 box.
- Select an editable cell and enter a number. Fixed clues cannot be changed.
- Red outlines identify duplicate numbers in a row, column or box. They do not identify every incorrect answer.
Controls
- Tap a cell and a number, or use arrow keys to move the selection and number keys to enter a digit.
- Pencil toggles notes in empty cells; N switches pencil mode. Erase, Backspace or Delete clears a cell or its notes.
- Hint points to a region, then explains each deduction. Choose Place to fill one proved number. Undo restores the previous entry and notes.
Nine fixed levels keep the original 46-, 39- and 32-clue starters, followed by two hidden-single, two locked-candidate and two naked-pair practice boards. Each addition has one solution and a checked deduction route using its named technique after simpler rules stall. Other solving approaches may differ; these are not certified human difficulty ratings. Free play is unchanged and usually has 36–40 clues.
Progress is saved in this browser on this site when storage is available. Clearing site data can remove it. There is no cross-device sync, and internet access is needed to load the game.
Frequently asked questions
What is a hidden single?
A digit has just one possible cell in a row, column or box, even if that cell has other candidates. Example: if 7 can appear only at row 2, column 5 in row 2, place 7 there, even if your notes in that cell also contain 3 and 8.
How do locked candidates work?
A digit confined to one row or column inside a box cannot occur elsewhere on that line. Example: if all candidates for 4 in the top-left box are in row 2, remove 4 from row 2 outside that box. The reverse also works: if every candidate for a digit in a row or column lies in one box, remove that digit from the other cells in that box.
What is a naked pair?
Two cells in the same row, column or box each have exactly the same two candidates. Those digits must occupy the pair, in either order. Example: if two cells in row 5 each allow only 2 and 8, remove 2 and 8 from every other cell in row 5. You cannot yet decide which paired cell is 2.
Does Hint explain a deduction?
Yes. Hint calculates candidates from your current entries, points to a region and explains singles, locked candidates or naked pairs one step at a time. It never treats pencil notes as the complete candidate list. Reading a hint changes no entries or notes; choose Place to fill a proved number, then Undo if needed. Conflicts must be checked first, and these techniques may not find a next number. Hints are counted only when you choose Place.