🧩Play Sudoku

Sudoku arrived in Japanese puzzle magazines in the 1980s, went global through a British newspaper in 2004, and has been the default commuter puzzle ever since. It contains no arithmetic at all despite being made of numbers — swap the digits for nine colours and the puzzle is identical. What it actually tests is constraint propagation: the discipline of noticing what a placement rules out.

Every puzzle on this page is generated fresh in your browser the moment you open it, and each one is verified to have exactly one solution before you ever see it. That verification is the part most casual implementations skip, and it matters: a grid with two solutions cannot be finished by reasoning, only by guessing, which turns the whole exercise into a coin flip.

Three difficulties are on offer, and the difference between them is simply how many clues are left standing — forty for Easy, thirty-two for Medium, twenty-six for Hard. Clues are removed in rotationally symmetric pairs, which is why the finished grid has the balanced look of a newspaper puzzle rather than a random scatter of numbers.

The board helps without solving anything for you. Selecting a cell dims its row, column and box so you can see the constraints at a glance, matching digits are highlighted across the grid, and a number that conflicts with one of its peers turns red the instant you place it. Pencil marks are available for the harder grids, and placing a digit automatically clears that note from every cell it can no longer occupy.