What is Sudoku?
Sudoku is the classic 9×9 logic puzzle. On Cognitive Train, the standard game can also be used for brain training and cognitive training focused on logic, attention, working memory, and systematic problem-solving. Using Sudoku for cognitive training does not change the game itself: the board is still divided into nine 3×3 boxes, and some cells already contain numbers (the clues). Your task is to fill every empty cell so that each row, each column, and each 3×3 box contains all of the numbers 1 through 9 with no repeats.
How to play:
- Choose a difficulty and how many puzzles you want to solve, then click Start Puzzle
- Tap or click a cell to select it, then tap a number button below the grid
- On desktop, you can also type numbers directly and move between cells with arrow keys
- Press Backspace, Delete, or the ✕ button to clear a cell
- Blue cells are given clues and cannot be changed
- The puzzle completes automatically the moment the grid is filled correctly
Difficulty levels:
- Easy (~40 clues): Plenty of starting numbers — most cells can be solved by simple scanning
- Medium (~32 clues): Requires cross-checking rows, columns, and boxes together
- Hard (~27 clues): Fewer clues force deeper elimination chains and candidate tracking
Solving tips:
- Scan for the most frequent numbers first — if 7 already appears seven times, the last two are usually easy to place
- Work box by box: check which numbers are missing from a 3×3 box, then use the rows and columns crossing it to eliminate positions
- Look for cells with only one possible value ("naked singles") — filling one often unlocks several more
- Every puzzle here is generated with exactly one solution
Scoring:
- Total Time: How long the full session took
- Avg per Puzzle: Total time divided by puzzles solved
- Hints Used: Each hint fills one correct cell — fewer is better