Sudoku Strategy: Candidates and Certain Placements
Learn to distinguish a pencil candidate from a digit forced by the row, column and box. These techniques explain decisions; they are not a promise of a particular solve time.
Play Sudoku →These tips follow the order in which the techniques get harder, which is also the order the hint button uses
These tips follow the order in which the techniques get harder, which is also the order the hint button uses. Each one is a way to remove candidates or find a digit with certainty. Learn them in this order and the levels of this game will open one after another.
Start with notes, but not everywhere
Start with notes, but not everywhere. On easy puzzles you can often see the digits directly. On medium and harder puzzles, write notes: for each empty cell, the digits not yet present in its row, column and block. It takes a minute, but every technique below works on notes. The game keeps them tidy: placing a digit removes it from the notes of every cell that sees it.
Tip 1: the single candidate
Tip 1: the single candidate. Look for a cell with only one note left. That digit must go there. After every placement, the notes around it shrink, and new single candidates appear. On easy puzzles this alone takes you a long way.
Tip 2: the only place in an area
Tip 2: the only place in an area. Pick a digit, say 7, and a block. Where could a 7 go in that block? If only one cell can take it, because the other cells already see a 7 in their row or column, the 7 goes there, even if that cell has other notes too. Do the same for rows and columns. Scanning one digit across the whole grid, block by block, is the fastest way to solve easy and medium puzzles. Players often call this cross-hatching.
Tip 3: locked candidates
Tip 3: locked candidates. Sometimes a digit inside a block can only go in one row of that block, even if you do not know which cell. Then that digit cannot appear anywhere else in that row outside the block: remove it from those notes. It also works the other way round: if in a row a digit can only go in cells of one block, it cannot go elsewhere in that block. Medium puzzles in this game always need this step at least once.
Tip 4: pairs
Tip 4: pairs. If two cells in the same area have exactly the same two notes, say 3 and 8, then those two digits belong to those two cells, in some order. No other cell of that area can hold a 3 or an 8, so remove them. The hidden version is just as useful: if two digits can only go in the same two cells of an area, those cells cannot hold any other digit. Hard puzzles need a pair or a triple.
Tip 5: triples
Tip 5: triples. The same idea with three cells and three digits. The cells do not each need all three notes; it is enough that together they hold only those three digits. Triples are harder to spot, so look for areas with few empty cells first.
Tip 6: the X-wing
Tip 6: the X-wing. Choose a digit and look at the rows. If in two rows that digit can only go in the same two columns, it forms a rectangle. Whichever way it falls, the two columns each get that digit in one of these rows, so the digit can be removed from all other cells of those two columns. The same pattern works with columns and rows swapped.
Tip 7: the XY-wing
Tip 7: the XY-wing. Find a cell with two notes, X and Y. It is the pivot. Now find two cells it sees: one with X and Z, one with Y and Z. Whatever the pivot becomes, one of those two wings becomes Z. So any cell that sees both wings cannot be Z. This pattern hides well; the hint highlights all three cells when it is the next step.
Tip 8: the swordfish
Tip 8: the swordfish. The X-wing with three rows and three columns. If a digit in three rows can only go in the same three columns, it can be removed from the other cells of those columns. Expert puzzles in this game need an X-wing, an XY-wing or a swordfish, and never anything harder.
General habits
General habits. Keep your notes complete before you look for advanced patterns, because a missing note can hide a pattern or fake one. After every placement, scan the row, column and block of the new digit: the next move is usually nearby. When you are stuck for a long time, the hint costs nothing on the first three uses and shows you which technique to look for. And if you make a mistake, relax: it never ends the game, and undo takes any step back.
Rules and one browser example checked 29 October 2026. A full manual win, physical-phone interaction and midnight rollover were not verified. Advertising rewards are unavailable.