Hidden Single
A digit with just one possible home in a row, column or box — even though that square still has other options.
What it is
A Hidden Single starts with a digit, not with a special-looking square. Pick the 8 and look across one row, column or box. If the 8 can go in only one empty square, it belongs there. That square may still allow other digits, which is why the move is hidden.
How to spot it
Pick one digit, then look at one row, column or box. Ask: “Where can this digit go?” If only one empty square remains, place it. Start with a box when you are learning — it is compact and easy to scan.
Worked example
One question per step: follow the 8 in the highlighted row.
Step 1 of 4: Look at the highlighted row
The 8 is still missing. It has to appear once somewhere in this row.
Why it matters
Hidden singles are the workhorse of easy and medium puzzles, and they are the technique beginners most often overlook because they only look at cells with few candidates. Learning to scan by digit rather than by cell roughly doubles the number of moves you can find without notes.
Practise now
Solve a puzzle where this technique decides the game
Frequently asked questions
How is a hidden single hidden?
The cell shows several candidates, so it does not look special. The insight comes from the digit's perspective: within that row, column or box the digit has nowhere else to go. Once you place it, the cell's other candidates simply vanish.
Which unit should I check first?
Boxes usually pay off fastest, because a box is compact and blocking lines are easy to see. Many solvers scan boxes digit by digit, then rows and columns when the boxes run dry.
Can a cell be both a naked and a hidden single?
Yes. If a cell has exactly one candidate and that digit also fits nowhere else in the unit, both descriptions apply. It makes no difference to the move — the digit still goes in.
Put it to use
Where you will meet it
This pattern is the backbone of easy grids. Start one and you will use it within a few moves.
Play EasyStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
Open the solverPrefer paper? Ready-made Easy sets as a PDF.Print puzzles
Finished reading? Mark it done and the learning path remembers where you got to.