A little space
for a curious mind.

4ool means “Tools for All.” Here, that means a good puzzle whenever you have a moment.

Six games. Your own pace.

Choose from Sudoku, Pipes, Takuzu, Nonograms, Shikaku and Hashi. Learn a new set of rules or settle into an old favorite. There are no accounts, daily streaks or leaderboards. Each new puzzle is made on your device.

Thoughtfully generated

Our independent TypeScript engines use seeded algorithms, constraint solvers and solution counting. A puzzle is accepted only after its solution and difficulty pass the engine’s checks. Difficulty is a consistent estimate of clue structure and solver effort, not a guarantee of how challenging you will find a particular board.

Built for the small moments

Play with a touchscreen, mouse or keyboard. Switch between light and dark themes. Use hints when you need a nudge, and undo when a move doesn’t work out. Progress and statistics stay in your browser.

Acknowledgments

We studied the algorithms and documentation of Simon Tatham’s Portable Puzzle Collection, which is published under the MIT license. Our game engines and interface are independently implemented; no original artwork, branding or C/WASM engine binaries are included.

Find practical tools and guides at 4ool.com, or support the project through Buy Me a Coffee.