Online Sudoku Game

Sudoku needs no introduction: a 9x9 grid split into nine 3x3 boxes, some cells already filled in, and one rule to follow — every row, column and box has to end up with the digits 1 through 9, each appearing exactly once. No arithmetic, no luck, just working out what has to go where by elimination.

This version keeps the classic format and lets you choose a difficulty before you start — Easy, Medium or Hard, based on how many starting digits the grid gives you. Clicking a digit highlights every matching number on the board, which makes it easier to spot where it can and can't go next.

Controls

• Click an empty cell, then click a number in the on-screen number pad to fill it in
• Use the small candidate-number buttons to pencil in more than one possible digit for a cell you're not sure about yet

Tips

• Start with rows, columns or boxes that already have the most digits filled in — they narrow down fastest
• If a number can only fit in one cell within a box, place it even if that cell still has candidates too
• Pencil in candidates instead of guessing when you're stuck between two or three options — it keeps your options straight without losing progress