Cross Sums FAQ

Cross sums are number crosswords. A grid of white and dark cells is filled with digits 1–9 instead of letters. Dark clue cells give the total for the run of white cells that starts beside or below them, and each run must add up to its clue without repeating a digit. The puzzle is solved when every across and down run matches its total.

Yes. Kakuro is the Japanese name for the same puzzle, which is also sold as cross sums, cross-totals, or a number crossword. The rules are identical: digits 1–9, no repeats in a run, and each run adds up to its clue. This game uses the cross sums name and the standard Kakuro rules.

Yes. crosssums.app is free with no download, no account, and no paywall. The puzzle runs entirely in your browser on desktop and mobile.

Select a white cell and enter a digit from 1 to 9. Every run of white cells must add up to the clue in the dark cell at its start, and no digit may repeat inside a run. Because each cell sits in one across run and one down run, you solve by finding digits that satisfy both sums at once.

A clue turns green when its run is complete and correct. When every clue is green, the puzzle is solved.

A digit cannot repeat within the same run, but it can appear again elsewhere in the grid, including in a crossing run. For example, a two-cell run with the clue 8 can be 1+7, 2+6, or 3+5, but never 4+4, while a 4 in some other run is fine.

Yes. Each puzzle is generated on your device and checked with a solver to confirm there is exactly one valid fill. If the random layout would allow more than one, the generator pre-fills and locks a few cells until the solution is unique, so you never have to guess.

The size is the playable area, not counting the row and column of clue cells. 5×5 has short runs and suits beginners, 7×7 adds longer runs and more crossings, and 9×9 can have runs up to nine cells long and needs chained deductions. Times and streaks are tracked separately for each size.

Look for runs with only one possible set of digits. In two cells the clues 3, 4, 16 and 17 are forced; in three cells 6, 7, 23 and 24 are forced. Place or note those digits, then check the runs that cross them.

The tips page has a table of the unique combinations for runs of two to six cells.

Notes lets you pencil small candidate digits into a cell instead of committing. Hint fills the selected cell with its correct digit and locks it. Check highlights any digits that differ from the solution. Using a hint means the solve will not count towards your best no-hint time.

A digit is marked red when it repeats within a run, when a run is full but does not add up to its clue, or when a partial run already adds up to more than its clue. Red means a rule is broken, not that the digit is necessarily wrong for the final solution — use Check for that.

Yes. The board, number pad, and tools are designed to fit on one phone screen in portrait. Tap a white cell, then tap a number. Pencil notes and undo are one tap away.

Best times, best no-hint times, solve counts, streaks, your last grid size, and the sound setting are saved in your browser on this device. They persist across refreshes and are not uploaded anywhere. An unfinished puzzle is not saved; if you start a new one after making moves, the streak for that size resets.

No. There is nothing to install and no sign-up. Open the page and press Play. The game works in current versions of Chrome, Edge, Firefox, and Safari.

Use the speaker button above the board or press M. The preference is remembered on your device. All sounds are generated in the browser, so there are no audio files to load.