Sudoku

📖 Strategy guide: Which Sudoku techniques our Easy to Expert puzzles really need

How to play

Fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. Tap a cell, then a number. Tap the same number again to clear it. Cells that clash with another turn red.

Notes, undo and hints

Switch on Notes (or press N) to pencil candidate digits into a cell; placing a digit clears that candidate from its row, column and box. Undo takes back as many moves as you like. A hint fills one cell with the correct digit; the selected cell if it is wrong or empty, otherwise the first wrong one.

Daily puzzle

The daily puzzle for each difficulty is the same for everyone and changes at midnight UTC. New puzzle gives you an unlimited supply beyond that. Every puzzle is generated with exactly one solution. Easy and Medium almost always fall to singles; on Hard and Expert, a puzzle sometimes needs a pair, a wing or a short what-if test — the strategy guide shows how often and how.

Getting faster

• Scan a digit at a time: where can the 7 go in this box, given the 7s in the rows and columns crossing it?
• Look for cells with only one candidate left (naked singles) and boxes where a digit fits in only one cell (hidden singles). Easy and medium puzzles almost always fall to those two ideas alone.
• On hard and expert, pencil marks pay off: pairs and triples of candidates that lock each other out are where the breakthroughs come from.