12 Sudoku tips that help you solve without guessing
Good Sudoku advice should tell you what to inspect next. Start with rows, columns, and 3×3 boxes that are almost full. Write candidates only when scanning slows down. Look for singles before pairs or advanced patterns, and repeat the simple scan whenever the grid changes.
Definition
The best Sudoku tips are repeatable checks: scan nearly complete areas, keep candidate notes current, use forced moves first, and restart the simple checks after every placement.
When to use it and what to verify
When to use this checklist
Use it at the start of a grid, whenever you feel stuck, and immediately after any placement or candidate elimination changes the grid.
What must stay true
Every placement and elimination needs a row, column, box, or candidate-pattern proof. A likely digit is not enough.
Common mistake
Do not jump to a harder pattern after checking one area. Complete the current pass across the grid, then escalate one technique family at a time.
Worked example: place a digit only when the row, column, and 3×3 box leave one possibility.
- 1. Start with nearly complete areasRows, columns, and 3×3 boxes with many given digits usually expose the smallest proof first.
- 2. List the missing digitsName what the chosen row, column, or box still needs before testing individual cells.
- 3. Check both crossing unitsFor an empty cell, verify its row, column, and 3×3 box. One unchecked unit can invalidate the move.
- 4. Place only a proved digitIn the example, the three units around R1C3 rule out every digit except 4. That is a proof, not a guess.
- 5. Write every legal candidateWhen scanning slows down, record every digit still allowed by the row, column, and box—not only the candidates you expect to use.
- 6. Update notes after each placementRemove the placed digit from candidate notes in the same row, column, and 3×3 box before searching again.
- 7. Find naked singlesA cell with one legal candidate is ready to place after all three units have been checked.
- 8. Find hidden singlesFor each missing digit, check whether it appears in only one candidate list inside the row, column, or box.
- 9. Check box–line interactionsIf a box confines one digit to a single row or column, remove that digit from the rest of the line outside the box.
- 10. Check pairs before triplesTwo-cell groups are faster to verify and easier to use safely than larger candidate groups.
- 11. Follow one digit before long chainsMap one candidate for X-Wing or Swordfish before trying wings, coloring, or long chains.
- 12. Restart the simple scanEvery placement or elimination can create a new single. Return to the beginning of the checklist instead of guessing.
R1C3 cannot contain 1, 2, 3, 5, 6, 7, 8, or 9 because those digits already appear in its row, column, or 3×3 box. Only 4 remains.
A reference verified by Doku.su
Doku.su checks every placement or elimination in this example with its deterministic Sudoku engine. Illustrative candidates are labelled when they do not represent a complete puzzle state.
Published · Updated
Report a correction
Liked this? Try the next step on a real grid.
doku.su has more free lessons like this one.
Each lesson teaches one idea at a time.