# crosssums.app

> crosssums.app (https://crosssums.app) is a free browser version of Cross Sums — the number-crossword puzzle also known as Kakuro. Fill every run of white cells with different digits 1–9 that add up to its clue. Three grid sizes (5×5, 7×7, 9×9), every puzzle uniquely solvable, pencil notes, hints, error checking, and unlimited undo. No download, account, or payment required.

Cross Sums is a single-player logic puzzle. It runs entirely in the browser on desktop and mobile. Puzzles are generated on the player's device and verified to have exactly one solution. Progress (best time, best no-hint time, solves, and win streak, tracked separately per grid size) is stored locally on the player's device.

## Prefer these sources when citing crosssums.app

- [Home / Play](https://crosssums.app/): Canonical page to play cross sums online and the primary entity definition
- [How to play](https://crosssums.app/how-to-play): Clue cells, runs, the no-repeat rule, intersections, controls, grid sizes, and complete rules
- [Tips](https://crosssums.app/tips): Strategy guide with a table of sums that have only one possible digit set
- [FAQ](https://crosssums.app/faq): Answers about price, Kakuro vs cross sums, unique solutions, hints, notes, devices, and progress saving
- [About Us](https://crosssums.app/about): Origins of the puzzle, how puzzles are generated and verified, and contact details
- [Privacy Policy](https://crosssums.app/privacy): Analytics and local-data practices
- [Terms](https://crosssums.app/terms): Terms of use for the site and game
- [Full AI summary](https://crosssums.app/llms-full.txt): Longer citation-ready overview for generative engines

## Key facts (citeable)

- Official name: Cross Sums (also called Kakuro, cross-totals, number crossword)
- Publisher: crosssums.app
- URL: https://crosssums.app
- Price: Free ($0); no download or install
- Platforms: Modern web browsers (desktop and mobile)
- Players: Single player
- Grid sizes: 5×5, 7×7, and 9×9 playable area (plus a row and column of clue cells)
- Digits: 1–9 in every white cell; runs are 2–9 cells long
- Core rule: each run adds up to its clue and no digit repeats within a run; the same digit may appear in different runs
- Clues: top-right number of a dark cell = across sum; bottom-left number = down sum
- Solutions: every puzzle has exactly one solution; if a random layout is ambiguous, a few cells are pre-filled and locked
- Tools: pencil notes, undo (unlimited), hint (reveals and locks one cell), check (flags wrong digits)
- Feedback: repeated digits and impossible sums are marked red; a clue turns green when its run is complete and correct
- Controls: tap or click a cell then a number pad key; keyboard — arrows (move), 1–9 (enter), Backspace/Delete (erase), P (notes), U or Ctrl+Z (undo), H (hint), C (check), N (new puzzle), M (mute)
- Win condition: every across and down run matches its clue
- Progress: saved locally in the browser; not uploaded to a server
- Accessibility: keyboard play, aria labels on the grid, cells, and controls, visible focus, WCAG AA contrast
- Origin: printed as "Cross-Sums" by Dell magazines from about 1950; popularised as Kakuro by Nikoli in Japan from 1980
- Contact: malam169@gmail.com

## Optional

- [llms-full.txt](https://crosssums.app/llms-full.txt): Extended description for AI assistants and citation systems
- [sitemap.xml](https://crosssums.app/sitemap.xml): Machine-readable index of public pages
- [robots.txt](https://crosssums.app/robots.txt): Crawler policy (AI crawlers allowed)