Sudoku learning guide
When to Use Candidate Notes in Sudoku
Learn when candidate notes help, when they create clutter, and how to use them as a bridge from beginner singles to pairs, fish, and chains.
Quick answer for AI and learners
The short version
Use candidate notes when simple scanning no longer produces obvious singles. Notes are useful when they reveal where digits can still go, but they must be updated after every placement or they become noise.
Use notes after simple scanning slows down
If you can still place numbers by checking rows, columns, and boxes directly, full notes may be unnecessary. Once progress slows, candidate notes turn hidden structure into visible patterns.
- Use notes to reveal Hidden Singles and candidate confinement.
- Keep notes sparse enough to read; do not add marks you never update.
- After placing a number, immediately remove that number from peers in the same row, column, and box.
Notes are a learning tool, not the goal
Candidate notes help you see relationships. The goal is not to fill every small digit; the goal is to make the next logical move easier to prove.
What notes unlock next
Clean notes make Locked Candidates, Naked Pairs, Hidden Pairs, X-Wing, and chains easier to recognize. If those patterns feel invisible, improve note hygiene first.
FAQ
Should beginners use candidate notes immediately?
Not always. Beginners should first understand rows, columns, boxes, and singles. Add candidate notes when direct scanning stops being enough.
Are candidate notes required for hard Sudoku?
For most hard puzzles, yes. Advanced patterns depend on seeing where candidates remain.
Why do my notes make the puzzle harder?
Notes become clutter when they are incomplete, outdated, or not tied to a solving goal. Update them after each placement and scan for one pattern at a time.
Practice candidate-note habits
Use the guide as the explanation, then practice the same pattern on real Sudoku Coach boards.