Master the art of pencil marks (candidate numbers) in Sudoku. Learn why keeping notes is essential for solving intermediate and advanced puzzles.
Using the "Pencil Icon (Notes Mode)" on our site allows you to type up to 9 small candidate numbers inside a single cell. These small numbers are called "Candidates" or "Pencil Marks".
In easy puzzles, you can often immediately determine where a single number goes. However, in Medium to Expert puzzles, you frequently encounter situations where a cell could be either a 2 or a 7 (with no immediate way to know which). Keeping track of multiple possibilities in your head becomes overwhelming. By jotting down candidate numbers, you can visualize possibilities and eliminate invalid numbers as you solve other parts of the grid.
While writing down every candidate is a valid strategy, filling the entire board with numbers can feel messy. A good rule of thumb for beginners is to start noting cells when they are narrowed down to 2 choices (Pairs) or 3 choices (Triples).
