Beginner
Notes in Sudoku
A core Sudoku solving technique for beginner players
What are notes (pencil marks) in Sudoku?
Notes - Also called pencil marks or candidate lists - Are small digits written inside an empty cell to record which numbers could still legally go there. A cell's note set is the list of digits not yet eliminated by the cell's row, column, or 3×3 box.
Notes do not solve the puzzle for you. They give you a structured record of possibilities so that advanced techniques like Obvious Pairs, Hidden Pairs, and X-Wing can be applied systematically.
When to start using notes
| Difficulty | Do you need notes? | Reason |
|---|---|---|
| Easy | Rarely | Most cells can be solved by direct elimination |
| Medium | Often helpful | Some cells need candidate comparison |
| Hard | Almost always | Pairs and triples require tracking candidates |
| Expert – Extreme | Essential | X-Wing and Swordfish are impossible without notes |
How to maintain accurate notes
- Fill all notes at once - Before solving, do a full pass and write every candidate for every empty cell.
- When you place a digit in a cell, immediately remove that digit from the notes of every cell in the same row, column, and box.
- When a cell's notes reduce to a single digit, it becomes an Obvious Single - Place it.
- Use our in-game Notes mode (pencil icon or N key) to toggle candidate entry on the board.
- Review your notes periodically for cells that have silently become singles after other placements.
Notes are not cheating. Every professional and competitive Sudoku solver uses candidate tracking. On paper, players use a pencil; on screen, you use the notes mode. Using notes is the mark of a systematic solver, not a weak one.