- Auto-candidate mode fills in all valid candidates for every empty cell automatically
- Fast pencil mode lets you quickly enter candidates without switching between digit and note mode
- Both features speed up setup — but understanding what they do keeps your logic sound
- Auto-candidates that update automatically after each placement are the most useful
- Relying on auto-fill too early can prevent you from developing manual candidate awareness
What Auto-Candidate Mode Does
Auto-candidate mode (also called "auto-notes," "candidate fill," or "smart pencil" in different apps) scans the grid and fills in every valid candidate for every empty cell at once. Instead of manually entering small digits in each cell, the app calculates which digits are still legal given the current row, column, and box constraints and displays them automatically.
On Sudoku.by, you can activate notes mode and use the auto-fill option to populate candidates. After each digit you place, the app removes that digit from the candidates of all peer cells automatically.
What Fast Pencil Mode Does
Fast pencil mode allows you to tap a digit to enter it as a candidate note without explicitly switching from "answer" mode to "note" mode. It reduces the number of button taps required to manage candidates, making pencil-mark entry significantly faster in practice.
When to Use Auto-Candidates
| Situation | Recommendation |
|---|---|
| Beginner learning basics | Do NOT use — learn to identify candidates manually first |
| Medium puzzle, comfortable with basics | Use for initial setup, then manage updates manually |
| Hard/Expert puzzle where setup is time-consuming | Use freely — saves time without obscuring logic |
| Speed-solving or timed practice | Always use — manual setup wastes competition time |
The Learning Risk
Beginners who rely on auto-candidates from the start miss a crucial learning step: the process of manually identifying which digits are possible in each cell builds pattern recognition that makes later techniques visible without notes. If you cannot mentally estimate which candidates a cell has without looking at auto-fill output, you will struggle with advanced patterns that require quick visual scanning.
Spend your first 20–30 puzzles filling candidates manually. After that, use auto-candidate freely. The how to play guide covers all note-taking features available on the site.