Fill every row, column, and three-by-three box with the digits 1 through 9, without repeats. Starting clues stay fixed. You can correct entries, use a hint, and leave the puzzle unfinished when your break ends.
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Fill each row, column, and 3 × 3 box with the digits 1–9 without repeats. Bold digits are fixed clues. Select a cell, then a number. Conflicts highlight duplicates; the absence of a conflict does not prove an entry is correct. Hint fills one cell with its solution value. Erase clears the selected entry; Undo restores the previous move. New puzzles have a unique solution.
Every square belongs to a row, a column, and a box. A proposed digit cannot repeat in any of those three groups. Looking only across the row misses restrictions coming from above, below, or another part of the box.
Starting clues and your own entries have different visual treatments. If an entry duplicates a number in its row, column, or box, the interface marks the conflict. That is a useful rule check. It is not a complete proof system: an entry can avoid every visible duplicate and still be wrong for the puzzle solution.
Look for a group with very few empty squares. If a column has eight different digits, identify the missing digit and check its remaining square. Before entering it, verify the row and box too. A simple deduction is enough; you do not need to begin with an advanced named technique.
You can also look for the only place a digit fits inside a box. Several squares might accept multiple candidates, yet only one could accept a seven. That is a different situation from a square that accepts only one possible digit. Both can produce a justified placement when all the relevant restrictions are checked.
A candidate is a digit that has not yet been ruled out. When you enter a confirmed number, review candidate lists in the same row, column, and box. Outdated notes can make an eliminated option appear available.
Keep tentative ideas separate from confirmed deductions. Filling several squares based on an unproved guess can make the board look productive while hiding the original uncertainty. If you are testing a possibility, remember which later choices depend on it. One well-supported placement gives you a cleaner starting point for the next decision.
First, return to the selected square and read its three groups again. A restriction in the column may eliminate a digit that looks perfectly reasonable in the row. Check the fixed clues as well as your own entries.
Second, choose the correction control that matches your intention. Erase clears the selected entry. Undo returns to a previous action. If you moved the selection after entering a number, those two controls may affect different squares. Read the position before using them repeatedly.
Third, ask a specific question before using a hint. A hint places the correct value in a square. Once it appears, inspect what that new digit rules out nearby. This gives you a way back into the puzzle without pretending the hint was a deduction you made yourself.
The main board has nine rows and nine columns. Practice starts with more givens while retaining a unique solution. Changing modes does not mean the previous puzzle was completed; the boards and their local results remain separate.
Progress stays in this browser. Another phone or browser has separate data, and clearing site storage can remove a saved board. The timer pauses when you leave the tab or open help. Finishing one row without visible conflicts is progress, but the game records a win only when the complete grid is correct.
Tap a square and use the on-page number controls to enter your choice. You do not need to open the phone keyboard for every placement. On a computer, use digit keys, arrow keys to move the selection, and Backspace to erase.
If you want a larger-print layout or a four-by-four puzzle, choose a page that actually provides that experience. Changing a heading does not make the numbers larger or turn a 9×9 grid into a beginner 4×4 board. This main game is 9×9. It is entertainment, without a promise to improve general memory, treat a condition, or replace another activity.
New puzzles are checked for a unique solution.
No. An entry can follow the visible no-repeat rules and still differ from the final solution.
Erase clears your selected entry. Undo goes back to the previous action.
It fills a square with its correct value so you can continue.
No. This main board is 9×9 with 3×3 boxes. A 4×4 variant needs a separate playable board.