Classic 9×9 Sudoku with easy, medium and hard boards, notes mode, hints, undo, and a timer with personal bests. Play free in the browser.
Sudoku is a number placement puzzle. Fill a 9×9 grid so that every row, column, and 3×3 box contains the digits 1 through 9 with no repeats. No maths needed — it's pure logic from start to finish.
Sudoku trains logical reasoning. Every cell you fill is based on a rule, not a guess. You scan for what must be true given the numbers already placed. This step-by-step deduction is the same thinking used in science and law.
It also trains focus. A single lapse in attention causes an error that can take minutes to undo. Regular Sudoku play is linked to better sustained attention in adults of all ages.
Spatial working memory is used too. You hold the grid's state in your head and update it as you fill in numbers. This is the same memory system used in navigation and visual planning.
Sudoku is one of the most studied brain games. Older adults who play regularly score higher on tests of processing speed and reasoning. It's easy to learn but stays challenging as difficulty rises.
The key benefit is that it demands active engagement. You can't zone out and still solve the puzzle. Every moment of play is focused mental work.
Start with the rows, columns, and boxes that have the most numbers already filled in. The more clues you have, the easier it is to work out what's missing.
Use pencil marks. Write small candidate digits in empty cells. Cross them off as you rule them out. This stops you from holding too much in your head at once.
Look for naked singles — cells where only one digit is possible. These are free answers. Find them before trying harder techniques.