Sudoku techniques: What to look for when you get stuck
Choose sudoku techniques by the deduction you need: Singles, naked pairs, locked candidates and X-Wing, with explained examples and practice exercises.
Choose a technique by the question it answers
Sudoku techniques prove placements and candidate eliminations. This catalogue helps you decide what to inspect when progress stalls in one area of the grid. If the rules are still new to you, start with the general learn-sudoku route. Here we assume you recognise rows, columns and boxes, and organise moves by the information they use. You do not need to learn every technique name before playing. Understanding one deduction, recognising its boundaries and applying it reliably is more useful than memorising a list of shapes without knowing why they work.
Direct placements
- Naked single
One cell with only one possible digit.
- Hidden single
One digit with only one place within a unit.
Eliminations in units and intersections
- Naked pairs
Two cells reserve the same two digits.
- Locked candidates
Follow one digit from box to line or line to box.
Patterns across several lines
- Sudoku X-Wing
Two rows and two columns restrict the locations of one digit.
Look for a direct placement first
Begin by asking which digits remain possible in a cell. A naked single answers that question with one digit. Then change the question and ask where one digit can go within a unit. A unique position gives you a hidden single, even if that cell contains several pencil marks. These techniques complement each other. Switching between cells and digits can reveal a move you missed while scanning the board in only one way. After a placement, update the connected row, column and box before inspecting the next position.
Eliminate candidates before placing a digit
A naked pair uses two cells in one unit with exactly the same two candidates. Those digits are reserved for the pair and can be removed from the rest of the shared unit. Locked candidates follow one digit through a box-line intersection. Two or three positions can remain open, while their confinement excludes that digit from other cells. The immediate result of either technique may simply be a shorter candidate list. Return to singles after the elimination: An intermediate technique often makes a straightforward placement available again.
Look across the grid with X-Wing
Once your notes are reliable and you can explain pairs and intersections, try X-Wing. Its rectangular form compares the possible locations of one digit in two rows or in two columns. Matching locations force eliminations in the crossing units. You need to look beyond a single box, but the reasoning still follows the ordinary rule against repeating a digit. Four similar-looking corners are insufficient: The lesson identifies the extra positions that break the argument. This catalogue offers a learning order, rather than a universal difficulty scale that applies to every puzzle.
Give your next action a reason
When many empty cells have no notes, review candidates before searching for advanced patterns. With complete notes, choose one digit or unit and look for a specific technique. If it does not appear, change your focus without forcing an elimination. Each lesson supplies a local example and an explained answer; these models are not complete grids for you to finish. In a real game, explain which condition you checked and which cell changes as a result. Useful assistance is reasoning you can reconstruct afterwards. Return to the learning introduction whenever you need a reminder of the rules or board controls.