Solve the standard nine-by-nine Sudoku by using every row, column, and three-by-three box together. Start with missing digits and only-place deductions, then use candidate restrictions to eliminate alternatives. This guide distinguishes a correct conclusion from an entry that merely avoids an immediate duplicate, and explains clear, undo, and hint controls.
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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.
A standard Sudoku has nine rows, nine columns, and nine three-by-three boxes. Fill every row, column, and box with the digits 1 through 9, without repeating a digit in any of those groups. Break Club’s main board uses this standard size. Its starting clues are fixed; the numbers you enter are the part you can revise as your reasoning develops.
Every cell belongs to three groups at once. Checking its row alone is insufficient if the digit is already in its column or box. The arithmetic total of a group is not a substitute for the rule either. The sequence 1, 1, 3, 4, 5, 6, 7, 9, 9 adds up to 45 but repeats 1 and 9 while omitting 2 and 8. Sudoku requires the complete set without repetition, not merely the right sum.
A conflict indicator can tell you that an entry repeats a digit already visible in its row, column, or box. The absence of that warning does not certify that the entry belongs to the puzzle’s solution. A cell may have several locally permitted candidates, only one of which can lead to a valid completion of the whole grid.
In a constructed Break Club example, the upper-left cell initially accepted a 5 without a visible duplicate, while the puzzle’s unique solution required a 3. Adding the 5 left no complete solution compatible with the other clues. This example illustrates the limitation of a local duplicate check; it is not a reading of the board currently open on your phone. Before committing an uncertain digit, ask what removes the alternatives rather than relying on the fact that the interface has not highlighted an error.
A nearly complete group provides a small, checkable problem. Suppose a column reads 1, 8, 6, 7, blank, 2, 3, 9, 5 from top to bottom. Comparing that list with 1 through 9 shows that 4 is missing. The blank is in the fifth row, so check its row and box as well before entering the 4.
That extra check matters when some of the eight visible values are your own earlier entries. If one is wrong, the apparent missing digit of the column may not establish a valid overall solution. Original clues and player entries have different roles in your evidence. When a group has two or more blanks, a missing-digit list can narrow the possibilities, but it does not necessarily place each digit. Keep the unresolved candidates separate until another constraint determines their locations.
A hidden single asks where one particular digit can fit within a group. Several cells in a box may each allow multiple digits, yet only one of those cells may be allowed to contain 7. If all other possible locations for 7 are excluded by their rows or columns, that remaining cell must contain it.
This differs from a naked single, where one cell has only one possible digit. Both can produce a justified entry, but the search direction is different. For the hidden single, choose a missing digit and inspect every empty cell in its row, column, or box. For the naked single, choose a cell and inspect all remaining digits. Do not conclude that a digit is unique merely because it appears once in an incomplete set of notes you made yourself. The elimination needs to cover every relevant empty location.
Suppose two cells in a row can contain only 3 and 9, and both cells are restricted to exactly that pair. One must contain 3 and the other 9, even if their order is not yet known. Other cells in that row cannot contain either digit. This can reduce another cell to a single remaining candidate without first choosing which member of the pair goes where.
The restriction “only 3 and 9” is essential. If one of the two cells might also contain 5, the argument does not establish an exclusive pair. Likewise, two cells that merely include 3 and 9 among several other candidates do not reserve those digits. Work from the full set of row, column, and box constraints. You can reason through candidates without assuming the main interface provides a particular pencil-mark feature; an explanation of a technique is separate from a claim about available controls.
Sometimes all remaining locations for a digit within one box lie in the same column. That digit must appear somewhere in that portion of the column, so it can be excluded from the column’s cells outside the box. You have learned where the digit cannot go without deciding which of the remaining cells inside the box contains it.
For instance, if the only two possible locations for 6 in a box are both in its left column, a cell farther down that same column, outside the box, cannot also contain 6. Check that all other locations inside the box really have been ruled out. This technique depends on the shared box and column, not on two candidate marks looking close together. After an elimination, revisit affected groups; a new single may appear, but it should be justified by the updated constraints rather than placed automatically in your explanation.
Clear removes the editable entry in the selected cell. Undo returns to the preceding action. If you entered a questionable number earlier and then worked elsewhere, these controls do different things. Clearing the selected old entry can preserve later work, while repeated undo may also reverse decisions you intended to keep.
Before using either control, identify the cell or action you actually want to revise. Fixed starting clues cannot be erased. A hint supplies a correct value for a cell and can help you continue when you are stuck, but the supplied value is assistance rather than proof that your own previous reasoning established it. After accepting help, compare that value with its row, column, and box so that the next decision rests on the new information.
Break Club checks newly generated main-board puzzles for a unique solution. That property concerns the starting puzzle; it does not make every locally legal choice a correct one. A completed board still needs every row, column, and box to contain 1 through 9 without repetition. Filling all the blanks is progress only if the finished arrangement satisfies those constraints.
On a phone, take time to distinguish the active cell from its highlighted row or box before entering a digit. If the selected position is not the one you intended, correct that selection instead of treating the resulting number as new evidence. You can leave a puzzle unfinished and return to the reasoning later. A productive next step may be one carefully explained digit, a candidate you can exclude, or a correction to an earlier assumption; it does not have to be an entire solved grid.
After entering a justified digit, revisit its three groups before moving to a distant part of the puzzle. That placement may remove one candidate from several cells or leave a single location for another digit. Follow the consequence of the information you actually added, without assuming every nearby blank must now be solvable. If nothing else becomes forced, choosing another promising group is a valid next step rather than a reason to fill the nearest blank speculatively.
No. It means the digit does not currently duplicate a visible digit in its row, column, or box. It may still be incompatible with the full solution.
New main-board puzzles are checked to preserve one solution. That does not make every locally permitted entry correct.
Clear removes the selected editable entry. Undo reverses the preceding action, which may concern a different cell.
It supplies a correct value for a cell. The supplied value is assistance, not proof that your previous reasoning derived it.
No. The main game uses a nine-by-nine board with three-by-three boxes. A smaller format requires a separately identified variant.