Sudoku· CardHearth
Sudoku9x9 gridfill 1-9 with no repeatsevery puzzle solvable by logic
How to play, tips & FAQ
How to play Sudoku
Every CardHearth Sudoku is solvable by pure logic — you never have to guess, and each puzzle has exactly one solution, verified by a solver at every difficulty. Fill the 9×9 grid so every row, every column, and every 3×3 box contains the digits 1 through 9 exactly once. Tap a square, then tap a number — or use your keyboard: arrows to move, digits to fill, Backspace to erase. Bold numbers are the puzzle's given clues and can't be changed; conflicts light up red the moment two matching digits share a row, column or box.
Notes, hints & mistakes
Toggle Notes (✎ or P) to pencil candidate digits into empty squares — placing a real digit automatically erases that candidate from the squares it rules out.Hint (H) reveals the correct digit for your selected square. TheMistakes counter ticks up whenever an entry disagrees with the unique solution, so you always know how clean your solve was. Undo is unlimited.
Strategy basics
Start with scanning: pick a digit that appears often and check which rows, columns and boxes still need it — intersections with one empty square are free wins. When scanning stalls, switch to pencil marks and hunt for naked singles (a square with one candidate) and hidden singles (a digit with one home in a row, column or box). Harder puzzles reward working box by box and keeping notes scrupulously current.
Frequently asked questions
Do CardHearth Sudoku puzzles have unique solutions?
Yes — every puzzle is generated and then verified by a solver to have exactly one solution, at every difficulty. If logic alone seems to run out, there is always a deduction available; no guessing is ever required.
What changes between Easy, Medium, Hard and Expert?
The number of starting clues: Easy begins around 40 givens, Medium around 34, Hard around 29, and Expert around 25. Fewer clues mean longer deduction chains and heavier use of pencil marks.
How do pencil marks (notes) work?
Toggle Notes on the number pad (or press P), then tap digits to mark candidates in a square. Notes are tidied up automatically: placing a digit clears that candidate from the same row, column and box.
Can I share a puzzle with a friend?
Yes. Every puzzle has a number shown next to the timer, and the Share button copies a link that opens the identical puzzle at the same difficulty — first to finish wins.
Need a change of pace? Deal yourself someKlondike Solitaire,Spider, orFreeCell — or defend your streak in theDaily Challenge.