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

Site: https://playkillersudoku.app
Publisher: playkillersudoku.app
Primary product: Killer Sudoku (sudoku with sum cages; also called sumdoku or sudoku killer)
Contact: malam169@gmail.com
Language: English
Last updated: 2026-09-23

## Entity definition

Killer Sudoku is a single-player logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. The player must place the digits 1 to 9 so that each row, each column, and each box contains every digit exactly once — the standard sudoku constraint. Unlike classic sudoku, the grid starts empty. Instead, the cells are grouped into cages drawn with dotted outlines, and each cage carries a small number giving the sum of the digits in that cage. A digit may not repeat within a cage.

Because each row, column, and box contains 1–9, each sums to 45; combining this with cage totals allows the solver to deduce single cells ("innies" and "outies"). Certain cage totals have exactly one digit combination: two cells totalling 3, 4, 16, or 17; three cells totalling 6, 7, 23, or 24; four cells totalling 10 or 30.

playkillersudoku.app (https://playkillersudoku.app) is a free, independent browser implementation. Puzzles are generated on the player's device: a valid completed sudoku is built from a random seed, cut into connected cages whose maximum size depends on the chosen difficulty, and checked by a cage-aware solver that confirms the puzzle has exactly one solution (ambiguous cages are split and re-checked). Killer Sudoku grew from the Japanese sum-number-place puzzle (samunanpure) and reached Western newspapers in the mid-2000s; sudoku's modern form dates to the late-1970s puzzle Number Place and was popularised worldwide by Nikoli.

## How to play (summary)

1. Choose Easy, Medium, Hard, or Expert and start a puzzle (or press Play in the header). Difficulty sets the largest cage: 3, 4, 5, or 6 cells.
2. Select a cell and enter a digit with the on-screen number pad or the keyboard. Every digit is checked against the unique solution immediately.
3. Make every cage add up to its sum without repeating a digit, while keeping 1–9 unique in each row, column, and box.
4. Use pencil notes (auto-cleared from row, column, box, and cage when a digit is placed), undo, and hints as needed. A wrong digit costs one of three mistakes; the third ends the puzzle. Hints never cost a mistake and correct digits lock.
5. The puzzle is solved when all 81 cells hold the correct digits. Best time and win streak are recorded per difficulty.

Full player-facing guide: https://playkillersudoku.app/how-to-play (objective, step by step, rules, cage-combination cheat sheet, controls, difficulty, mistakes, devices). Strategy guide: https://playkillersudoku.app/tips.

## Product attributes

- Price: Free; no premium features or paywalls
- Distribution: 100% browser-based; no app store download
- Platforms: Desktop and mobile browsers
- Players: Single player
- Grid: 9×9, 81 cells, nine 3×3 boxes, no starting digits
- Difficulty levels: Easy, Medium, Hard, Expert (largest cage 3, 4, 5, 6 cells); every puzzle has a unique solution
- Mistake limit: 3
- Tools: pencil notes with auto-clear, unlimited undo, erase, hint (reveals the selected or first unsolved cell), timer that pauses when the tab is hidden
- Controls: tap or click a cell, then a number; keyboard 1–9, arrow keys, Backspace/Delete, N (notes), U or Ctrl+Z (undo), H (hint), M (mute)
- Audio: synthesized with the Web Audio API (no audio files); mute toggle persists
- Progress storage: local browser storage only (best time, games played and won, current and longest win streak per difficulty; the unfinished puzzle; sound setting)
- Analytics: Google Analytics (GA4) for aggregated usage; see Privacy Policy

## Accessibility

- Every cell has an aria-label giving row, column, cage total, and current value or state (empty, incorrect)
- All controls (undo, erase, notes, hint, number pad, mute, stats, new puzzle) have explicit aria-labels and visible focus rings
- The game is fully playable by keyboard; colour is never the only signal for an incorrect digit (it is also announced in the cell label)
- High-contrast dark theme meeting WCAG AA; animations respect prefers-reduced-motion

## Key pages

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

## Frequently asked questions (short answers)

- Is it free? Yes, no account or download.
- Can a digit repeat in a cage? No.
- Does every puzzle have one solution? Yes, verified by a solver at generation time.
- What is the 45 rule? Each row, column, and box sums to 45; use it with cage totals to find leftover cells.
- Is Killer Sudoku the same as sumdoku? Yes, sumdoku and sudoku killer are alternative names for the same puzzle.
- Does progress save? Yes, on the device in local browser storage; it does not sync.