Sudoku Tricks: 7 Techniques That Take You Past the Basics
There is a wall in sudoku, and most players hit it around the same place: they can solve easy and medium puzzles quickly, then stall on hard ones with a half-filled grid and no obvious next move. The wall is not intelligence - it is technique. Below are seven techniques in the order they should be learned, because each one assumes the previous ones are already automatic.
Technique 1: Scanning (Rows, Columns, Boxes)
For each digit from 1 to 9, sweep every row, column, and 3x3 box and ask where that digit can legally go. In easy puzzles this fills most of the grid. Do not skip this because it feels basic - on hard puzzles you will still find placements this way that you missed while looking for something cleverer.
Technique 2: Candidates (Pencil Marks)
Once scanning stalls, write the possible digits in every empty cell. This looks like busywork and is not: candidates turn sudoku from guessing into set logic. Every technique below is a statement about candidates, so none of them work without them written down.
Technique 3: Naked Pairs
If two cells in the same row, column, or box both contain exactly the same two candidates, those two digits are locked into those two cells. You can remove both digits from every other cell in that unit.
Example: two cells in a row both show only 4 and 7. Then no other cell in that row can be 4 or 7. This often cascades - removing a candidate from one cell frequently turns a three-candidate cell into a naked pair, which unlocks a third, and so on.
Technique 4: Hidden Pairs
The inverse of a naked pair. If two digits appear as candidates in exactly two cells within a unit - and nowhere else in that unit - those two cells must hold those two digits, regardless of what else is written in them. You can then delete every other candidate from both cells.
Hidden pairs are harder to spot than naked pairs because you are scanning for a digit pattern rather than staring at a crowded cell. The habit that finds them: for each digit, count how many cells in the unit still allow it. Two is the magic number.
Technique 5: Pointing Pairs (Box-Line Interaction)
If a digit can only go in one row within a 3x3 box, then that digit must be somewhere in that row - so it cannot appear elsewhere in the same row outside the box. The reverse also works: if a digit is confined to one box within a row, eliminate it from the rest of that box.
This is the highest-value technique for medium puzzles. It is also the one most players never learn, which is why they stall on puzzles that are actually straightforward.
Technique 6: X-Wing
The first genuinely advanced technique. Find two rows where a digit can only appear in the same two columns. Those four cells form a rectangle - and the digit must occupy one pair of opposite corners. Therefore that digit can be eliminated from every other cell in both columns.
Technique 7: Swordfish and Beyond
A swordfish is an X-wing extended to three rows and three columns. It is rare, it is slow to spot, and it matters only on the hardest puzzles. Learn it when X-wings stop being enough - not before. Beyond swordfish you reach chains and forcing nets, which are better suited to software than to a paper puzzle.
When to Stop and Guess
This is the part most guides skip. If you have exhausted every technique above and the puzzle still has multiple valid solutions from your current state, you may be looking at an under-constrained puzzle rather than a failure of skill. Genuine sudoku has one solution; puzzles published in newspapers occasionally do not.
- If two cells in a unit both accept the same two digits with no way to distinguish them, that is a guess.
- If a guess is required, pick the cell with the fewest candidates - it minimizes the damage of being wrong.
- Note your guess before making it. Without a record you cannot unwind a wrong branch.
Sudoku Techniques FAQ
What is the fastest way to get better at sudoku?
Write candidates in every cell and learn naked pairs and pointing pairs. Those three habits alone move most players from medium to hard puzzles, because they turn the grid into a set-logic problem instead of a guessing game.
Do I need to write candidates?
On easy puzzles no. On medium and above yes - every advanced technique is expressed as an operation on candidates, so without them written down you cannot apply any of them reliably.
What is the difference between a naked pair and a hidden pair?
A naked pair is two cells that contain only the same two candidates. A hidden pair is two digits that appear in only two cells of a unit. Both lock those digits into those cells; they are found by looking at opposite things.
Are hard sudoku puzzles always solvable by logic?
Properly constructed ones are. Puzzles that require guessing are either badly made or extremely high difficulty. If you have candidates written and every technique fails, consider that the puzzle may have multiple solutions.
Is sudoku good for your brain?
It trains working memory and pattern recognition, and the effect is strongest while you are still learning new techniques. Once a puzzle type becomes routine the cognitive benefit drops, which is a reason to keep increasing difficulty.
Start Playing
Our Sudoku page runs free puzzles in the browser with candidate marks and difficulty tiers. If you are new to the game entirely, start with our beginner rules guide before touching the techniques above.
