The break-in: the first deduction
The first step a solver can make is the break-in. Good setters place it on purpose.
How it works
A solver facing a fresh grid needs somewhere to start. The break-in is that first forced step: a cell or a line that the rules and the givens settle on their own.
Some puzzles have several starting points, which makes them friendlier. Some have one hidden break-in, which makes the opening a puzzle in itself. Both are choices the setter makes.
In this sudoku, the break-in is a hidden single: a row that needs a digit and has only one cell that can take it.
Designing the opening
When you set clues first, the break-in is the first thing you place. Put down just enough givens to force one step, then solve from there.
When you set from a solution, find the break-in afterward by solving your own puzzle as a solver would. If the first step is hard to find, that may be the point. If it is a guess, it is a flaw.
Worth memorizing
The break-in is the first forced step.
The rules and the givens settle it alone.
More starting points make a friendlier puzzle.
One hidden break-in makes a harder opening.
Find your break-in by solving your own puzzle.
Solve it the way a stranger would.
Practice
0 of 4 rightWhich cell can a solver fill first?
Which cell can a solver fill first?
Which cell can a solver fill first?
How many cells can a solver fill at the very start?