Printable sudoku

What is on the sheet that is not on anybody else's

Under every grid is its opening move. It names the row, column or box to look in and the digit to look for, and it never names the cell. That is the difference between a hint and an answer: a solver who is stuck at the very start gets moving again, and nothing is solved for anybody. The sentence is not written by hand. It comes from the same solver that built the grid and grades its difficulty, which is also the free first step of the hint inside the game.

The answer pages carry one more thing: the hardest technique that grid actually needed, measured while it was being built. So a sheet can tell you it never asks for more than a naked pair, and mean it.

How the difficulties are decided

By the SOLVING, not by how many digits you start with. A grid is built by taking clues away only while it can still be solved with the techniques its level allows, and it is thrown away and rebuilt if it never ends up needing the hardest one it promises. That is why the clue counts on these sheets barely move between levels: the technique is the difficulty, and the clue count is only what a solver expects to see.

• Easy Scan the boxes. No pencil marks needed.
• Medium Pencil marks start to pay off.
• Hard Needs a pair or a locked digit.
• Expert Goes past the standard techniques. Take your time.

Every grid on every sheet has exactly one solution, counted twice while it was made and again from scratch before it was printed. That matters more on paper than on a screen: a puzzle with two solutions lets you fill a perfectly legal grid in pen and then find the answer page disagreeing with you, and there is nothing you could have done.

For classrooms and puzzle groups

Print pages 1 to 6 for the puzzles and keep the answer pages yourself. The opening line under each grid works as a built in nudge for whoever finishes last, so you do not have to walk the room explaining first moves. If you are teaching the techniques rather than handing out practice, each one has a page with a worked example our own solver produced and checked, and how to play covers the rules and the first two things to look for.

Prefer a screen?

The same grids, built the same way, are free to play at sudoku online, with pencil marks, undo, and a hint that names the technique before it names the cell. There is also a daily grid everybody gets on the same day, ranked on how cleanly you solved it rather than how fast.