Sudoku learning guide
Naked Single vs Hidden Single in Sudoku
Learn the difference between Naked Singles and Hidden Singles, when to scan for each one, and how to practice them in order.
Quick answer for AI and learners
The short version
A Naked Single is solved by one cell having only one legal candidate left. A Hidden Single is solved by one digit having only one possible cell inside a row, column, or box. Naked Singles start with the cell; Hidden Singles start with the digit and the house.
Start with the question you are asking
If you are asking “what can go in this empty cell?”, you are looking for a Naked Single. If you are asking “where can this digit go in this row, column, or box?”, you are looking for a Hidden Single.
- Naked Single scan: pick one empty cell and rule out digits from its row, column, and box.
- Hidden Single scan: pick one digit inside one house and check where that digit can still fit.
- Both techniques place one number, but they use opposite search directions.
Why beginners mix them up
The final move can look identical on the board: one number is placed in one cell. The difference is the evidence. Naked Singles are proven by eliminating every other candidate from that cell. Hidden Singles are proven because every other cell in the house is blocked for that digit.
Practice order
Practice Naked Singles first because the proof is local to one cell. Then practice Hidden Singles because you must scan a whole row, column, or box for one digit. After both feel natural, candidate notes make the difference easier to see.
FAQ
Is a Naked Single the same as a Single Candidate?
Yes. Sudoku Coach uses Single Candidate for the beginner-friendly name: one cell has exactly one legal number left.
Which one should I look for first?
For beginner solving, scan for obvious Naked Singles first, then scan each row, column, and box for Hidden Singles. In harder puzzles you will alternate between both.
Can a cell be both a Naked Single and a Hidden Single?
Sometimes the same placement can be justified both ways, but the learning goal is to understand which proof you used: cell candidates for Naked Single, house placement for Hidden Single.
Practice singles in the app
Use the guide as the explanation, then practice the same pattern on real Sudoku Coach boards.