Sudoku
Classic 9×9 Sudoku in four difficulties, each puzzle made on your device with exactly one solution. Notes, hints that explain the technique, undo and an optional timer.
Open Sudoku →What is Sudoku?
A classic 9×9 Sudoku that runs entirely in your browser. Fill the grid so that every row, every column and every 3×3 box holds the digits 1 to 9 once each. Every puzzle is made on your device and checked to have exactly one solution, and its difficulty comes from the solving techniques it needs, not just from how many clues it shows. There are no adverts, no accounts, no sound and no scores, and it works offline.
How to use Sudoku
- Choose a difficulty — Easy, Medium, Hard or Expert. Picking a level starts a new puzzle at that level; New game makes another one at the same level.
- Select a cell and enter a digit — Click or tap a cell, then press a digit on the pad or your keyboard. Arrow keys move around the grid, Delete or Backspace clears a cell, and entering the same digit again removes it.
- Keep notes — Turn on Notes (or press N) to pencil in the digits a cell might hold; Shift with a digit adds a note without switching modes. Placing a digit removes it from the notes beside it.
- Check, or ask for a hint — Check strikes through any digit that does not match the solution. Hint fills in the next cell a person could find and names the technique that finds it.
Frequently asked questions
Does every puzzle have only one solution?
Yes. While a puzzle is made, a solver checks after every clue removed that exactly one solution remains, so it can always be solved by logic.
What makes Hard harder than Medium?
The techniques needed. Easy needs only singles; Medium adds pointing pairs, box/line reduction and naked or hidden pairs; Hard adds triples, X-Wing and XY-Wing; Expert needs a Swordfish or something deeper still.
How do the hints work?
The hint solves from your correct digits the way a person would and fills in the next cell it can prove, saying which techniques it used. If one of your digits is wrong, it points that out first.
Is my game saved?
Yes, in your browser on this device, after every move. Close the tab and come back later to carry on. Nothing is sent anywhere.
Tips
- Turn off "Show conflicts as you type" for a pen-and-paper feel, then use Check when you want to know how you are doing.
- The timer is off by default. When it is on, it pauses whenever you leave the tool or switch away from the page.
- Undo and redo (Ctrl+Z, Ctrl+Y) cover every move, notes included.