Plainoku uses Queens-style placement rules, not classic number sudoku. These short guides explain how to get started.
Cat Sudoku rules in one minute
Cat Sudoku keeps the placement logic of sudoku and swaps the numbers for cats and the boxes for coloured regions. Three rules do all the work:
- Every row holds exactly one cat. A five-row board needs five cats, not a cat in every square.
- Every column holds exactly one cat — same count, same idea.
- Every coloured region holds exactly one cat.
The rule people miss is the fourth one: no two cats may touch, including diagonally. A cat in row 3, column 3 rules out the other squares in its row and column, the rest of its region, and the eight squares around it — corners included. A square further along the same diagonal is not excluded for that reason alone.
That's the whole ruleset. There is no arithmetic, no number to add up, and every puzzle on this site has a single solution. If you have played LinkedIn's Queens or Star Battle, you already know the mechanic.
→ The three rules — the full statement, with the diagonal constraint explained.
How to play your first Cat Sudoku puzzle
Start on the 5×5 Easy board. Fewer squares make it easier to see how one placement changes its row, column, region and neighbours. Tap an empty square to place a cat; tap again to remove it. Press Mark to switch to crosses and tap squares you have ruled out. Erase and Undo fix mistakes, and Hint first removes an incorrectly placed cat if one is present; otherwise, it reveals one correct cat when you are stuck. The whole board is playable with a keyboard — arrows to move, Enter to place, N for Mark, Z to undo.
The workflow that matters is the second half: after every placement, scan what it just excluded. Placing a cat is the easy part; noticing what it closed off is where the puzzle gets solved.
→ How to play — the step-by-step version, including the board tools and keyboard controls.
The three techniques that solve most boards
Scanning the board is where beginners lose time. Sweep rows, columns and regions for a square that has only one option left, instead of staring at the whole grid at once. On a 5×5 board that habit helps you find the next move.
The hidden single is the highest-yield pattern: one square in a row, column or region that is the only place a cat can legally go. Find it and you have placed a cat with certainty. These turn up constantly on the larger boards.
Exclusion marks are your working memory. Marking a square you have ruled out stops you re-checking it, and the marks themselves show you when a region has been narrowed to one option. Crosses are manual notes — the board will not do this thinking for you.
→ Scanning the board · Find the only possible square · Use exclusion marks
Which Cat Sudoku board size should you start with?
The five board sizes are 5×5, 6×6, 7×7, 8×8 and 9×9. Their names — Easy through Master — describe size, not calibrated logical difficulty. A 9×9 board is not harder because the logic changes; there is simply more board to hold in your head at once. Most solvers notice the difference around 7×7, where scanning takes more discipline than instinct.
Start at 5×5 to learn the rules, move up when a board starts finishing itself, and try the daily Cat Sudoku — a fixed 6×6 puzzle for your device's local date — when you want a puzzle you did not choose.
→ Start a 5×5 Easy board · Play today's daily Cat Sudoku
Why play Cat Sudoku without ads?
Every puzzle on this site loads instantly in the browser. No ads, no pop-ups, no sign-up, no download, no time limit. Your progress and statistics stay in your own browser when storage is available.
Cat Sudoku is a genre that mobile app players know for one recurring complaint — mandatory ads between levels. This site exists so the puzzle does not come with that.