Beginner Sudoku Strategy
Candidate Notes
Notes record the digits that are still possible for a cell after row, column, and box checks.
Core concept
What it means
Candidate notes keep Sudoku from becoming a memory test. A note is valid only when the digit survives all three checks for that cell.
The important part is that this is not a guess. A good Sudoku move should explain why at least one digit is forced or impossible. Candidate Notes gives you that explanation by connecting the three checks that define the puzzle: row, column, and 3x3 box.
Use this technique slowly at first. Name the container or region you are studying, list the legal candidates, and only then place a final digit or remove a note. That habit keeps the board readable when harder puzzles make several deductions interact at once.
Pattern triggers
When to use it
Look for Candidate Notes when direct scanning slows down and you need a concrete reason to place a digit or remove a candidate.
- Cells with two candidates.
- Boxes where one digit appears as a candidate in only one cell.
- Old notes that became wrong after a placement.
Solving routine
Step-by-step method
Use this method slowly enough that every removal and placement can be checked against the grid.
- 1
Choose a crowded row, column, or box rather than the whole board.
- 2
For each empty cell, list only digits not already used in its row, column, or box.
- 3
Remove notes immediately when a related digit is placed.
- 4
Switch back to final-value mode when a cell has one candidate left.
Worked example
How it appears on a real board
A cell might start with candidates 2, 5, and 8. If an 8 is placed in the same column, remove 8 and keep only 2 and 5.
After the deduction, update related cells immediately. A single placement changes its row, column, and 3x3 box, and stale notes are the fastest way to create mistakes.
Accuracy checks
Common mistakes
Most Sudoku errors come from moving before all three units agree. Before placing a final digit, check the row, the column, and the 3x3 box.
- Adding every digit as a note without checking constraints.
- Keeping stale notes after a row, column, or box changes.
- Letting notes replace actual solving.
Practice checklist
Use it on your next board
On your next Medium board, annotate one 3x3 box fully, then solve from that box before expanding.
- Name the row, column, or box you are studying.
- Remove candidates only when a visible rule explains the removal.
- After a placement, update every affected note before scanning elsewhere.
- Use hints only as a nudge, then continue with auditable logic.