How to use Sudoku
- Pick a difficulty and start a puzzle.
- Fill cells with numbers 1–9 using mouse or keyboard.
- Use notes mode for candidates; watch conflict highlights.
- Complete the board so each row, column, and box has 1–9 once.
Worked examples
Concrete numbers and cases you can check against the tool above.
Notes on a medium puzzle
Fill pencil marks (notes) in a box when a digit has two or three candidate cells, then look for singles. Conflict highlights catch a 7 entered twice in a row. Easy puzzles are for warm-up; hard usually needs notes. This is a practice grid, not a daily newspaper reprint.
When to use Sudoku
Sudoku trains logic without a download or account wall. Difficulty levels plus notes and conflict highlights make practice sessions smoother on any device.
Common use cases
- Play a quick puzzle during a commute.
- Practice pencil-mark techniques with notes mode.
- Challenge yourself on hard difficulty.
- Use keyboard entry for faster solving on desktop.
Inputs and outputs
- In-browser Sudoku puzzle play (no file import required)
Privacy
This tool runs entirely in your browser. Your data never leaves your device — nothing is uploaded to our servers.
Frequently asked questions
- Can I take notes?
- Yes. Notes mode lets you pencil in candidate digits.
- Does it check mistakes?
- Conflict highlighting helps spot duplicates in a row, column, or box.
- Is progress saved to an account?
- Play happens locally in your browser session; no account is required.