How to Use Notes in Sudoku
Notes (pencil marks) are the working memory of a Sudoku puzzle. They help you track candidates in unsolved cells and make deeper patterns visible when direct moves run out.
Summary
Use candidate notes to keep hard boards organized and avoid guess-driven mistakes.
Table of Contents
What this technique is
Notes (pencil marks) are temporary candidate values used to track what may still fit in each unsolved cell.
When to use it
Use notes when direct placements slow down, typically from medium difficulty onward.
How it works
Record only valid candidates, clean them after each placement, and use updated notes to detect singles, pairs, and advanced patterns.
Step-by-step
- Add candidates only where direct placements are not available.
- After every placement, remove invalid candidates in the same row, column, and box.
- Re-scan for singles and pattern-based eliminations.
Example
Two cells in one unit with the same two candidates can reveal a naked pair once notes are kept clean.
What Notes Are
Notes are temporary candidate digits inside empty cells. They are not final answers; they are a representation system that makes real techniques like pairs, wings, and fish easier to detect.
When to Use Notes
Use notes as soon as direct moves slow down, especially in medium, hard, and expert puzzles where candidate interaction becomes the main source of progress.
How to Use Notes Well
Write only valid candidates, update notes after every confirmed placement, and focus on active areas first. Over-marking the entire board too early can reduce clarity instead of helping.
Why Notes Matter
Clean notes make advanced techniques easier to spot and reduce mental overload in dense puzzle stages.
Practical Note Discipline
Start with light notes in the most constrained zones, clean candidates immediately after each placement, and re-check for new singles right after every cleanup pass.
Common Mistakes
- Keeping outdated notes after major placements.
- Writing too many candidates without verification.
- Using notes as a replacement for logic scanning.
- Treating notes as permanent instead of flexible candidate state.
- Filling the whole board with noisy notes too early.
FAQ
What are notes in Sudoku?
Notes are candidate digits that show which values can still fit in a cell.
When should I start using notes?
Use notes when obvious placements run out, usually from medium difficulty onward.
Can too many notes hurt solving?
Yes. Messy or stale notes make the grid harder to read and should be cleaned regularly.