Hard Sudoku
24 to 26 givens, dug as deep as a board can go and still be logical.
Play hard sudokuUnlimited boards, generated fresh each time. Nothing here touches your streak. Or play today's daily sudoku — the same grid for everyone, once per day.
What makes a board hard
Difficulty here is the number of givens — the digits already on the grid when you start. These boards are dug down to 24–26 clues. Fewer givens means fewer places to anchor a deduction, which is what actually makes a grid hard.
Dug until one more removal would break the puzzle. Expect naked and hidden pairs, locked candidates, and stretches where nothing moves until you find one specific elimination. Still solvable without guessing — that constraint is enforced when the board is built.
No guessing, ever
Every board is built by removing digits one at a time and, after each removal, checking two things: that exactly one solution still exists, and that a logic solver can still reach it without backtracking. A removal that fails either test is put back. So there's never a point where the only way forward is to pick a number and hope — if you're stuck, a deduction exists and you haven't found it yet.
That's a stricter guarantee than "has a unique solution". Plenty of published sudoku have exactly one answer that no human technique will reach.
How this differs from the daily
The daily sudoku is one grid a day, the same for every player, and it feeds your streak, best times and win rate. This page is practice: unlimited boards at one difficulty, none of them recorded. Past dailies stay in the archive.
Other difficulties
- Easy Sudoku — Around 50 given numbers, and never a move you have to hunt for.
- Medium Sudoku — Around 38 givens. Singles run out; you start needing pencil marks.