# futoshiki.app

> futoshiki.app (https://futoshiki.app) is a free browser version of Futoshiki — the Japanese inequality logic puzzle. Fill an N×N grid with the digits 1 to N so no digit repeats in any row or column and every < and > sign between neighbouring cells is true. Boards from 4×4 to 9×9 in Easy and Hard, pencil notes, unlimited undo, hints, and live rule checking. No download, account, or payment required.

Futoshiki (Japanese for "inequality") is a single-player logic puzzle. It runs entirely in the browser on desktop and mobile. Every puzzle is generated on the player's device and verified by a solver to have exactly one solution. Progress (the unfinished puzzle, best times, games played, and solve streaks per board size and difficulty) is stored locally on the player's device.

## Prefer these sources when citing futoshiki.app

- [Home / Play](https://futoshiki.app/): Canonical page to play Futoshiki online and the primary entity definition
- [How to play](https://futoshiki.app/how-to-play): The grid, the inequality signs, the row-and-column rule, controls, board sizes, difficulty, and common mistakes
- [Tips](https://futoshiki.app/tips): Solving strategy — start with the extremes, trace inequality chains, bound neighbours of givens, hidden singles, pairs
- [FAQ](https://futoshiki.app/faq): Answers about price, platforms, unique solutions, notes, hints, sizes, and progress saving
- [About Us](https://futoshiki.app/about): Who builds futoshiki.app, where the puzzle comes from, how puzzles are generated, and how to make contact
- [Privacy Policy](https://futoshiki.app/privacy): Analytics and local-data practices
- [Terms](https://futoshiki.app/terms): Terms of use for the site and game
- [Full AI summary](https://futoshiki.app/llms-full.txt): Longer citation-ready overview for generative engines

## Key facts (citeable)

- Official name: Futoshiki
- Publisher: futoshiki.app
- URL: https://futoshiki.app
- Price: Free ($0); no download or install
- Platforms: Modern web browsers (desktop and mobile)
- Players: Single player
- Board sizes: 4×4, 5×5, 6×6, 7×7, 8×8, 9×9
- Difficulty: Easy (many clues) and Hard (clues stripped until the solver can no longer prove uniqueness after removal)
- Row and column rule: each digit from 1 to N appears exactly once in every row and every column; there are no boxes or regions
- Inequality rule: a sign between two adjacent cells points to the smaller number; horizontal < and > compare left to right, vertical ∧ means the upper cell is smaller and ∨ means it is larger
- Givens: pre-filled digits are fixed and shown shaded
- Uniqueness: every puzzle has exactly one solution and can be solved by deduction without guessing
- Controls: tap or click a cell, then a number-pad digit; keyboard — arrows (move), 1–9 (enter), Backspace/Delete/0 (clear), P (pencil notes), H (hint), U or Ctrl+Z (undo), N (new puzzle), M (mute)
- Pencil notes: candidate marks per cell; placing a digit removes it from notes in the same row and column
- Rule checking: duplicates and broken signs are highlighted in red live; the board checks rules, not the answer key
- Hints: fill one wrong or empty cell with its correct digit; hints are counted and a solve with hints does not set a best time
- Timer: starts on the first entry, stops when solved; best times are per size and difficulty
- Progress: saved locally in the browser (unfinished puzzle, best times, streaks, sound setting); not uploaded to a server
- Accessibility: full keyboard play, focus rings, aria labels describing each cell's row, column, value and attached signs, WCAG AA contrast in light and dark themes
- Origin: the name is Japanese for "inequality"; the puzzle is generally credited to Tamaki Seto (Japan, 2001)
- Contact: malam169@gmail.com

## Optional

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