Calcudoku

How to play Calcudoku

Fill the grid with the numbers 1 to its size: 1–4 on a 4×4 board, 1–5 on 5×5, or 1–6 on 6×6. Every row and column must contain each number once. There are no Sudoku boxes.

Each grid size has 32 original puzzle bases, with rotated and reflected layouts. The collection counts each base once; a new puzzle can revisit a base rather than promise endless new puzzles. Grid size is a choice, not a guaranteed difficulty rating.

Let the cage clues guide you

The outlined groups are cages. Their numbers must make the printed target using the cage operation. A single-cell cage gives that cell’s value. Addition and multiplication can use several cells. Subtraction and division use two: their difference or larger-divided-by-smaller ratio must match the target, in either spatial order.

A cage can contain the same number more than once when those cells are in different rows and columns. Repeats are still forbidden within any row or column. Cage sets respect this distinction; Calcudoku does not have a separate cage-wide no-repeat rule.

Numbers, notes and clear feedback

Choose a square and use the number pad, or type a digit. Notes switches to pencil marks; erase an entered value before adding notes to that square. Entering a value clears that square’s notes. Erase removes its value and notes. Pencil marks in other squares are kept for you to review.

Red cells show present row, column or cage-rule problems. Feedback checks the numbers you have entered; it does not mark a number wrong merely because it differs from a stored answer. An error-free partial grid is not a promise that every later choice will work.

Useful help, clearly labelled

Use Cage sets to see digit sets that fit the selected cage’s arithmetic and current row and column entries. Repeated digits are included when their positions permit them. These local sets do not guarantee a complete solution; pencil notes are not treated as restrictions.

Hint explains a checked deduction when one is available. If it instead supplies a verified solution value, the message calls it a reveal. A contradictory position gets a diagnosis without an invented forced value. Hint may also identify an entry that disagrees with the verified solution; the message labels that as a verified entry check. Hint and Cage sets both count as help, including after Undo or Restart.

A calm puzzle, at your pace

There is no time limit. Pause hides the puzzle and stops active time. Meaningful edits and help start the clock; simply selecting a square does not. A new puzzle can use 4×4, 5×5 or 6×6. The current board stays in place while you choose; Start confirms its replacement.

Undo and Redo revisit up to 200 actions. Restart clears the same puzzle as practice. Help and practice history remain recorded; replaying a finish or a transformed version of a previously solved puzzle does not duplicate original-puzzle progress.

Keyboard and small-screen play

Arrows move between squares. Number keys enter digits in range, Delete or 0 erases, N switches notes, U or Ctrl+Z undoes, Y or Ctrl+Shift+Z redoes, H asks for help and P pauses. Escape closes a panel or returns from full screen. Native size selection keeps its normal keyboard behavior.

The large number pad keeps play comfortable on a small screen. Full screen provides more room; Back to page restores your place on the page. Sound starts off, celebrations stay out of the grid, and motion follows your browser preference.

Your progress stays with you

Eight achievements recognise real cage and puzzle progress across the three grid sizes and the original puzzle collection. A clean finish needs no recorded help, Undo or Restart for that original puzzle. Saved puzzles include values, pencil notes, history and active time when browser storage is available. A persistent warning explains when saving is unavailable. No account is needed.

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