Expert sudoku is graded by the toughest techniques in the solver: Swordfish over three rows, XYZ-Wing or naked and hidden quads. These puzzles often look ordinary but stall quickly. When you are stuck, Hint fills the next cell that follows and says why.
How to use
- Pick a difficulty or today’s daily puzzle. Every puzzle has exactly one solution.
- Tap a cell, then tap a number on the pad. The small number under each digit shows how many are still missing.
- Turn on Notes to pencil in candidates. Placing a number removes it from the notes in its row, column and box.
- Stuck? Hint explains the next logical step and fills in one cell. Undo and Redo go back and forth through every move.
- Fill the grid so every row, column and 3×3 box contains 1 to 9 exactly once. Your game is saved automatically.
- Difficulty is graded by the techniques a solver needs: easy uses only singles, medium needs pairs or pointing, hard needs triples, X-Wing or XY-Wing, expert needs Swordfish, XYZ-Wing or quads. No puzzle ever requires guessing.
- The daily sudoku is the same for everyone on the same date. Medium on weekdays, hard on weekends.
- The timer pauses when you switch tabs. Each difficulty keeps its own game in progress, so you can switch freely.
- Printable sheets fit A4 and Letter paper, with up to 6 puzzles per page and an optional answer page.
Sudoku rules
Fill the 9 × 9 grid so that every row, every column and every 3 × 3 box contains the digits 1 to 9 exactly once. The given numbers cannot be changed. A proper sudoku has a single solution, which means every cell can be worked out by logic from the clues.
How the difficulty levels are graded
Each puzzle is solved by a step-by-step solver and graded by the hardest technique it needs. Easy needs only singles: a cell with one possible digit (naked single) or a digit with one possible place in a row, column or box (hidden single). Medium adds naked and hidden pairs and pointing pairs. Hard needs triples, X-Wing or XY-Wing. Expert needs Swordfish, XYZ-Wing or quads.
This is why two puzzles with the same number of clues can feel very different: what matters is which deductions you have to find, not how full the grid looks.
Solving tips
Scan each digit across the whole grid before writing notes; on easy puzzles this alone finishes the game. Turn on Notes when a cell has two or three candidates, and let the game clear them as you place digits. If you are stuck, Hint fills the next cell that can be placed and says why: the only spot for that digit in its row, column or box, or the only digit left for the cell.
Frequently asked questions
How do you play sudoku?
Put a digit from 1 to 9 in each empty cell so that no row, column or 3 × 3 box contains the same digit twice.
Does every sudoku here have one solution?
Yes. Every puzzle is checked to have exactly one solution, and none of them requires guessing.
What makes a sudoku hard?
The techniques it needs, not the number of clues. Hard puzzles need patterns such as X-Wing or XY-Wing; expert ones need Swordfish or XYZ-Wing.
What are notes or pencil marks in sudoku?
Small candidate digits you write in a cell while you are unsure. Placing a number removes it from the notes in its row, column and box.
Is the daily sudoku the same for everyone?
Yes. Everyone gets the same puzzle on the same date: medium on weekdays and hard on weekends.
Can I switch levels without losing my game?
Yes. Each difficulty keeps its own game in progress in this browser, and the timer pauses when you leave the tab.