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Sudoku strategies

Six moves solve every puzzle on this site. The first two finish every easy and medium puzzle. Hard puzzles add the next three, and expert puzzles need the last one, the X-wing, or a naked triple. Learn them in this order.

By Emre Özen, updated October 7, 2026. The diagrams show only the squares that matter; the rest of the grid is left blank.

1. Naked single

Look at one empty square and cross off every number in its row, column and box. If only one number survives, that's the answer. It's the first move everyone learns and the one you'll use most.

The highlighted square sees 1, 2 and 3 in its row, 4, 5 and 6 in its column, and 7 and 8 in its box. Only 9 is left.

2. Hidden single

Now flip the question. Pick a number and a box (or a row, or a column) that still needs it, and find every square where it could go. When the other squares are blocked, the number has only one home, even if that square could hold other numbers too.

The top-left box needs a 5. The 5s in rows 1 and 2 block those rows, and the 5s in columns 1 and 2 block those columns. Only the bottom-right square of the box is left.

Hidden singles are what make medium puzzles feel harder than easy ones. In 200 medium puzzles from our generator, 125 needed at least one; only 24 of 200 easy puzzles did.

3. Pointing pair

From here on, notes help a lot. When every possible spot for a number inside one box lies on the same row, that number has to end up in that part of the row. So it can't go anywhere else in that row, and you can cross it off the rest of the row. The same works with columns.

Inside the top-left box, 4 can only go in the two green squares, both in row 2. So 4 can be crossed off the other squares of row 2, shown in red.

This is the workhorse of hard puzzles: 197 of 200 hard puzzles from our generator used it at least once.

4. Naked pair

If two squares in the same row, column or box have the same two candidates and nothing else, those two numbers belong to those two squares. You don't know yet which goes where, but you do know neither number can appear anywhere else in that group.

Two squares in row 4 can only be 2 or 7. So 2 and 7 come off every other square in the row.

5. Hidden pair

The quieter cousin of the naked pair. If two numbers can only go in the same two squares of a group, those squares must hold those two numbers, so any other candidates in them can be erased.

In row 7, 3 and 6 fit only in the two green squares. Those squares must be 3 and 6, so their other notes (8, 1 and 9) come out.

6. X-wing

Pick a number. If in two rows it can only go in the same two columns, the four squares form a rectangle. Whichever way the number lands, it takes one corner in each of those columns. So it can't appear anywhere else in those two columns. It also works the other way, with two columns and two rows.

In rows 2 and 6, 3 can only go in columns 3 and 8. That rectangle means 3 comes off every other square in columns 3 and 8.

In our bank of 120 checked expert puzzles, 89 needed an X-wing. The other expert move, the naked triple, works like a naked pair with three squares and three numbers; 39 of those puzzles needed one.

What we leave out on purpose

There are fancier techniques with names like swordfish, XY-wing and forcing chains. You won't need them here. Our generator rejects any puzzle that can't be solved with the six moves above plus the naked triple, because a puzzle that needs trial and error stops being fun for most people. If you get stuck, the Hint button shows the next square and why.

Put it to work: play a hard sudoku, where moves 3 to 5 matter, or try expert once X-wings make sense.

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