Start with the three constraints
Every completed row contains the digits 1 through 9 once each. The same rule applies to each column and each 3 × 3 box. A number must fit all three groups at the same time. The starting clues are fixed references, so you cannot change one simply because a later entry conflicts with it.
For example, a blank square may accept a 7 in its row but share a column with another 7. That rules out 7 there. A useful candidate is a number still permitted after checking row, column, and box. A permitted candidate is not automatically the final answer; another deduction must establish why its alternatives do not work.
Find a small decision you can prove
Look for a square with only one remaining candidate. Another useful starting point is a digit that has only one available location within a box. If a box needs a 4 and all but one of its empty squares share a row or column with an existing 4, the remaining square must hold it.
After entering a proven value, revisit its row and column. That one addition may reduce another square to a single candidate. There is no need to hold the entire puzzle in your head. Work on a small relationship, record the result, and use the board itself as your reference for the next decision.
Use the on-screen large view deliberately
Make sure the intended square is selected before choosing a digit. Large cells can require moving around the board on a phone, so check the thick box boundaries and the current selection after scrolling. A square near the edge of the visible area may still have other box members outside that area.
Your browser’s standard zoom tools can provide further enlargement. They should not change the puzzle or create a new set of clues. If the view becomes awkward, restore your preferred zoom and identify a fixed starting clue before continuing. Readability involves both the size of the digits and enough context to know which group you are checking.
Check the printed puzzle before using paper
Select Print puzzle and inspect your browser’s preview. Check that the full grid and its starting clues fit on the sheet. Choose a paper size, orientation, and scale that leave the digits readable. Keep the grid together so you can follow each row and column without moving between separate sheets.
Pencil entries on paper do not update the browser’s puzzle. If you switch between paper and screen, compare the starting clues to confirm that you are using the same board. Use print preview before committing to a sheet, especially after changing paper size, margins, or scale; those settings affect the physical result.
Use support without a health or speed promise
A hint can provide a next step, but look at the row, column, and box afterward to understand its placement. Undo reverses an action, while erasing clears an editable entry; use the one that matches the correction you intend. If you prefer fewer cells, the separate 4 × 4 variant uses digits 1 through 4 and 2 × 2 boxes.
There is no completion time appropriate to a particular age, and one puzzle cannot assess your health. This is a recreational game, without a claim to treat memory problems or prevent a condition. Pause when you want, return to a manageable deduction, and choose the screen or paper presentation that actually feels readable to you.
Frequently asked questions
Can I play with large digits on screen?
Yes. The large-digit view is active on this page; browser zoom provides further enlargement.
Can I print the puzzle?
Yes. Select Print puzzle, inspect the browser’s preview, and print the grid. Pencil entries do not update the browser game.
Does the standard grid use digits 1–9?
Yes. Rows, columns, and 3 × 3 boxes each use 1 through 9.
Is there a smaller grid?
The separate 4 × 4 variant uses 1 through 4 and 2 × 2 boxes.
Is this a treatment?
No. The game makes no medical claim.