In a box, a digit fits only along one line: it goes from the rest of that line.

What to look for

Take one box and one digit. If every cell of the box where that digit can still go lies in the same row (or the same column), those two or three cells point along that line.

Why it works

The box needs the digit somewhere, and every choice is in that row. So the row’s copy of the digit is inside this box, and it cannot also be in the row’s cells outside it: cross it out there.

Practise it

Puzzles that need it: Medium sudoku

Play this puzzle from the start

On a real puzzle

8235357194641986235253573567492358123358614235792394235625713581723523589256429471638563125258479758934621

Pointing

In box 2, 2 can only be in column 6.

So 2 can go from the highlighted cells.

The cells that show the pattern are in amber, the cells it changes in green, and the candidates it removes are circled.

How it works

  1. Pick a variant and a difficulty, and play on the board: click or tap a cell, then a digit. Corner and centre marks, undo, a timer and hints are all there.
  2. Stuck? A hint names the technique a person would use next and highlights the cells that show it.
  3. To print, switch to Print: choose how many puzzles, which variants and difficulties, how many to a page, and where the answers go. Then print or download the PDF.

Everything runs in your browser and is free: no sign-up, nothing uploaded. Your game is saved in this browser, so you can close the page and carry on later.

What the difficulties mean

  • Easy: singles only (a cell with one possible digit, or a digit with one possible cell).
  • Medium: also pointing and box–line reductions.
  • Hard: also pairs, triples and quads.
  • Expert: also X-wings, swordfish, XY-wings, XYZ-wings and short chains.
  • Evil: also jellyfish and longer chains, and not just one: at least three advanced steps (fish, wings or chains) in every puzzle, except killer and consecutive ones, whose cages and bars do much of the work. Never guessing: every puzzle has exactly one solution, found by logic.

Every variant

Classic
Fill the grid so every row, column and box holds each digit once.
Killer
As classic, and the digits in each dashed cage add up to its sum, with no repeats in a cage.
Jigsaw
Every row, column and outlined shape holds each digit once.
Diagonal (X)
As classic, and both shaded diagonals hold each digit once too.
4×4 kids
Every row, column and box of four holds each symbol once.
6×6 kids
Every row, column and box of six holds each symbol once.
6×6 jigsaw
Every row, column and outlined shape of six holds each symbol once.
Even–odd
As classic; circles hold odd digits, squares even ones.
Windoku
As classic, and the four shaded boxes hold each digit once too.
Consecutive
As classic; a bar joins every pair of neighbours that differ by one, and no other pair does.
Thermo
As classic; digits rise from the bulb of each thermometer to its tip.
Arrow
As classic; the digit in each circle is the sum of the digits along its arrow (they may repeat if they don’t share a row, column or box).
Sandwich
As classic; the number outside each row and column is the sum of the digits between the 1 and the 9 in it.
16×16
Every row, column and box of sixteen holds each symbol once.

More sudoku