How to use notes (pencil marks) in Sudoku

Updated November 1, 2026

Notes, also called pencil marks, are small digits you write in a square to remember what it could still be. They are the difference between holding a puzzle in your head and having it in front of you. Used well they turn a stuck grid into one where the next move is obvious; used badly they bury the grid in clutter. This guide covers how notes work on Puzzle Temple, two ways to use them, and how to keep them honest.

How notes work here

• Press the Notes button, or the N key, to switch notes on. The number pad and your keyboard digits now add or remove small marks in the selected square instead of placing a digit. Press it again to go back to placing digits.
• Notes only go in empty squares, and a square can hold any combination of the nine digits.
• Notes are never checked. A wrong note does not count as a mistake and is not flagged, which makes them safe to experiment with, but it also means the game will not warn you when a note is wrong.
• When you place a digit in a square, that square's own notes are cleared. The notes in the other squares of its row, column and box are not touched, so removing that digit from them is your job. More on that below.
• Undo steps back through your last 50 moves, and note changes count as moves, so you can try a line of thought and take it back.

Style one: notes only where you need them

Solve with scanning for as long as it works, and only write notes when you stall. Then mark just the tight spots: squares that are down to two or three candidates. Two squares in a group with the same two marks is a naked pair, and you will see it at a glance.

This style keeps the grid readable and suits Easy, Medium and Hard, which are solved with singles. The cost is that you cannot see patterns in squares you did not mark, so when you are stuck for a long time, switch to the second style.

Style two: the full candidate grid

When singles run out, fill in every candidate for every empty square in the region you are stuck in, or for the whole grid. It takes a few minutes and it feels slow, but the harder patterns, such as naked pairs and locked candidates, are only visible when the candidates are all on screen. It is the approach Expert and Extreme usually call for. The techniques guide shows what to look for once the marks are in.

To fill a square correctly, work out which digits are missing from its row, its column and its box together. Whatever is not already in any of the three is a candidate.

Keeping notes clean

A note that should have been removed but was not is a common reason people find a "pair" that is not really one, or a "hidden single" that is not really hidden. Since the game does not tidy neighbouring notes for you, build a habit:

1. Place the digit.
2. Remove that digit from the notes of every square in its row, its column and its box.
3. Only then look for the next move.

If you ever find a contradiction, such as a square with no candidates left, a note was almost certainly left wrong earlier. Undo a few moves, or clear the notes in that area and rebuild them from the digits on the board.

Using notes to spot techniques

• Hidden single. In a row, column or box, look at one digit across all its notes. If it appears in only one square, it goes there.
• Naked pair. Two squares in the same group holding exactly the same two marks. Remove those two digits from the rest of the group.
• Pointing and claiming. A digit whose marks inside a box all fall on one line, or whose marks along a line all fall in one box.

Notes are a tool, not a goal. Use as few as the puzzle needs, keep them true, and clear them when a region is finished.