First Tips
Let's start by reviewing the basic rules of the game:
When to use it
Start every puzzle here, before reaching for any named technique.
Worked example
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Pick the digit that appears most often — here 5 — and mark the rows and columns it already occupies.
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Where those lines leave a box with a single free cell, the 5 must go there.
Common mistakes
- Guessing instead of proving a placement — a well-formed Sudoku never needs a guess.
- Filling a cell from its row alone without also checking its column and box.
Frequently asked questions
Where should I start a Sudoku?
With the digit that already appears most often: it has the fewest empty cells left and is easiest to place by scanning.
Do I have to write candidates?
Not at first. Place every digit you can by simple scanning, and only pencil in candidates once the easy moves dry up.