Sudoku Pencil Marks - How to Use Candidate Notes

Pencil marks are small candidate notes you place inside empty cells to show which digits are still possible. They are one of the most important tools in real sudoku solving because they make hidden structure visible. Once easy puzzles stop giving you obvious singles, notes prevent confusion and stop you from guessing.

How to Add Pencil Marks

For each empty cell, check the row, column, and box. Write down every digit from 1 to 9 that is not blocked. Those remaining digits are the cell's candidates. Repeat this across the whole grid if you want a full pencil-mark map.

Elimination Workflow

Whenever you place a number, update the candidates in all affected cells. Remove that digit from the same row, column, and box. Then rescan for new singles, pairs, or other patterns. This repeated cleanup is the heart of medium and hard sudoku.

When Not to Use Pencil Marks

You usually do not need notes for Very Easy or Easy Sudoku. They become much more valuable around Medium difficulty and above.

Using the Notes Feature in Our Sudoku

On our game board, switch to note mode before entering a digit. Use it to track candidates, then turn it off again when you want to place confirmed values. If you are learning advanced techniques, combine this page with the Sudoku Techniques guide.

Frequently Asked Questions

What are pencil marks in sudoku?

They are small candidate notes in empty cells.

When should I start using pencil marks?

Usually at medium difficulty, and definitely from challenging onward.

Should I use pencil marks on easy sudoku?

Usually not. Easy puzzles are often solvable without them.