About ClearSudoku

ClearSudoku does one thing: free sudoku in the browser, built around the solve itself. No account, no download, no popups between you and the board.

Why we built it

Two convictions shaped it, and the name follows from both. The first: the board comes first. A clean layout, generous touch targets, quick keyboard play, and nothing pushed between you and the grid, on any screen. The second: a difficulty label should be a promise. When ClearSudoku calls a puzzle hard, that claim rests on something measurable, and the next section explains exactly what.

Everything else about the site follows from those two decisions.

How the puzzles are made

Every puzzle here is generated offline, in large batches, long before you see it. Each one starts from a completed grid. The generator removes clues one at a time, and after every removal it checks that the puzzle still has exactly one solution. Any removal that would allow a second solution gets put back.

Then a second program solves the puzzle using only techniques a human could apply, from scanning up through forcing chains, in order from cheapest to most advanced. The hardest technique it needs becomes the puzzle's difficulty. A puzzle that cannot be finished with human logic gets thrown away, however interesting it looked, which is why no puzzle here ever requires guessing.

The result is a bank of just over 2,000 verified puzzles at each of the five difficulties, more than 10,000 in all, and every one of them re-checked for consistency, uniqueness and correct grading before publication.

What the labels promise

Difficulty labels mean the same thing every time. Easy means scanning and singles suffice. Medium adds locked candidates and pairs. Hard brings hidden sets and X-wings, expert brings wings, fish and coloring, and master demands forcing chains. The how to play guide teaches the whole ladder, and each play page teaches the techniques its own tier requires.

The player's side

The features are the ones a solver reaches for mid-puzzle: pencil marks with one-tap auto notes, three mistake-checking modes from purist to instant feedback, hints that fill the cell a logical solver would take next, and an undo that rewinds anything, restarts included. Your game autosaves on every move, one slot per difficulty, so you can close the tab mid-solve and pick the same board up tomorrow. Dark mode, full keyboard play and best-time tracking are all built in.

The defaults are tuned so that most players never need to open settings. If you do, the gear icon above the board holds every switch.

Your data

Your games, settings and stats live in your own browser and nowhere else. There is nothing to sign up for and nothing to sync. The privacy policy spells out the details, and it is a short read because there is so little to tell.