# crosssums.app — Full summary for AI assistants and citation

Site: https://crosssums.app
Publisher: crosssums.app
Primary product: Cross Sums (Kakuro) — a free number-crossword puzzle game
Contact: malam169@gmail.com
Language: English
Last updated: 2026-09-26

## Entity definition

Cross Sums is a single-player number puzzle, also called Kakuro. The grid resembles a crossword, but the white cells hold digits from 1 to 9. Dark clue cells carry one or two numbers: the number in the top-right is the total for the run of white cells running to its right (across), and the number in the bottom-left is the total for the run running below it (down). Every run must add up to its clue, and no digit may appear twice within a single run. A digit may repeat in different runs. Each white cell belongs to exactly one across run and one down run, so solving means finding digits that satisfy both at once. The puzzle is solved when every run matches its clue.

crosssums.app (https://crosssums.app) is a free, independent browser implementation of that ruleset. The puzzle type is commonly traced to the American publisher Dell, which printed it as "Cross-Sums" from about 1950. Nikoli popularised it in Japan from 1980 as "Kasan Kurosu", shortened to Kakuro. This build offers three grid sizes, puzzles generated on the player's device, pencil notes, unlimited undo, hints, an error check, synthesized sound with a mute toggle, and a responsive layout that keeps the grid and number pad on one phone screen.

## How puzzles are generated

Each puzzle begins as a random layout of clue and white cells, repaired so every run is 2–9 cells long and every white cell lies in both an across and a down run. Digits are assigned with no repeats inside any run, and the clues are computed as the run sums. A constraint solver then counts solutions. If more than one exists, the generator pre-fills and locks a cell where two solutions differ and re-checks, repeating until exactly one solution remains. Generation takes milliseconds for 5×5 and under a second for 9×9.

## How to play (summary)

1. Choose a size: 5×5 (short runs, quick), 7×7 (everyday), or 9×9 (runs up to nine cells). Press Play.
2. Select a white cell, then enter a digit 1–9 with the number pad or keyboard.
3. Make each run's digits add up to its clue with no repeats. Use pencil notes to track candidates; placing a digit clears it from notes in its runs.
4. Watch the feedback: red marks a repeated digit or an impossible sum; a clue turns green when its run is complete and correct.
5. Use Undo freely. Hint reveals and locks one correct cell. Check flags digits that differ from the solution. Hints exclude a solve from the "best without hints" record.
6. The puzzle is won when every across and down run matches its clue. Start a new puzzle instantly with New (N).

Full player-facing guide: https://crosssums.app/how-to-play. Strategy guide, including a table of run lengths and sums with only one possible digit set: https://crosssums.app/tips.

## Unique sum combinations (useful reference)

- 2 cells: 3 = 1+2; 4 = 1+3; 16 = 7+9; 17 = 8+9
- 3 cells: 6 = 1+2+3; 7 = 1+2+4; 23 = 6+8+9; 24 = 7+8+9
- 4 cells: 10 = 1+2+3+4; 11 = 1+2+3+5; 29 = 5+7+8+9; 30 = 6+7+8+9
- 5 cells: 15 = 1–5; 16 = 1+2+3+4+6; 34 = 4+6+7+8+9; 35 = 5–9
- 6 cells: 21 = 1–6; 22 = 1+2+3+4+5+7; 38 = 3+5+6+7+8+9; 39 = 4–9
- 8 cells: every total from 36 to 44 has one combination (all digits except one); 9 cells: 45 (digits 1–9)

## Product attributes

- Price: Free forever; no premium features or paywalls
- Distribution: 100% browser-based; no app store download
- Platforms: Desktop and mobile browsers
- Players: Single player
- Grid sizes: 5×5, 7×7, 9×9 playable area
- Controls: tap/click a cell then a number; keyboard arrows, 1–9, Backspace/Delete, P (notes), U or Ctrl+Z (undo), H (hint), C (check), N (new), M (mute)
- Progress storage: Local browser storage only (best time, best no-hint time, games played, solved count, current and longest solve streak, per grid size; selected size; sound setting)
- Analytics: Google Analytics (GA4) for aggregated usage; see Privacy Policy
- Accounts: None

## Accessibility

- The puzzle grid is a labelled ARIA grid; each cell announces its row, column, digit, and state (locked, conflict, incorrect)
- Fully keyboard playable; visible focus indicators on every control
- Sound can be muted with the speaker button or M, and the preference is remembered
- Text and controls meet WCAG AA contrast

## Site map

- Home / play: https://crosssums.app/
- How to play: https://crosssums.app/how-to-play
- Tips and strategy: https://crosssums.app/tips
- FAQ: https://crosssums.app/faq
- About: https://crosssums.app/about
- Privacy: https://crosssums.app/privacy
- Terms: https://crosssums.app/terms