Online Sudoku Game

Sudoku needs no introduction: fill the 9x9 grid so that every row, every column, and every 3x3 box contains the digits 1 through 9 exactly once. This is the same rule set as the newspaper puzzle, just playable straight in the browser with no pencil, no eraser marks, and no page to lose.

A session is untimed pressure in the best sense — there's a running clock, but nothing forces you to beat it. Start with the rows, columns, and boxes that already have the most numbers filled in, since those give away the most through simple elimination. As the grid fills in, later cells stop being guesses and start being certainties, which is the actual satisfaction of the puzzle: every completed board was solved with logic alone, never luck.

Controls

Click or tap a cell to select it, then click or tap a number to place it in that cell. Select a filled cell again to change what's in it.

Tips

• Scan one number at a time across the whole board — find every row, column and box where a digit is missing, and see how many cells it could possibly go in.
• Work the rows, columns and boxes that are already mostly full first; they leave the fewest open cells to reason about.
• When a cell can only hold one possible number once you account for its row, column and box, that's a certain placement — not a guess.
• If you get stuck, step back and re-scan for a different number instead of forcing a placement you're not sure of.

It's a good fit for a short break as much as a longer sit-down session — there's no level to fail out of, just a grid to work through at your own pace.