Find the Mistake Sudoku

Find the Mistake is a quick Sudoku puzzle: a half-finished board where one digit breaks the rules. You get five seconds to spot it before the answer is shown on the board.

How to play

1. Every row, every column and every 3×3 box can hold each digit from 1 to 9 only once.
2. Black digits were printed with the puzzle. Blue digits were filled in by a player.
3. Exactly one blue digit repeats a digit that is already in its row, column or box. That digit is the mistake.

How to find it faster

• Only suspect the blue digits. A printed digit can't be wrong, so the mistake is always one a player filled in.
• Take one blue digit at a time and sweep its row, then its column, then its box.
• Start with crowded rows and columns. The more digits a line holds, the more chances it has to repeat one.
• Look along the whole line. In our puzzles the repeated digit is always at least three cells away, never right next door.

Why it makes you better at Sudoku

Checking a digit against its row, column and box is the move behind every Sudoku technique, from the first single to X-Wings. The faster you see a repeat, the faster you see which digits a cell can't hold.