What is Hardest Sudoku?
The hardest Sudoku, objectively graded.
By The Hardest Sudoku Team · Last updated
TL;DR
Hardest Sudoku is a free web Sudoku trainer that goes up to the hardest puzzles ever rated, with every puzzle measured on the objective SE grade scale.
What is Hardest Sudoku?
Hardest Sudoku is a free web Sudoku trainer that goes up to the hardest puzzles ever rated. Every puzzle is measured on the objective SE grade scale — the difficulty is a number, not a marketing label. It reaches the legendary monster puzzles at the very top of that scale. Hints explain the next step; they never solve a cell for you. The tedious parts are handled for you, so you focus purely on the logic.
Our philosophy
Most Sudoku never gets hard enough — we go all the way up to the hardest; we measure difficulty directly and refine it with data.
- · The hardest Sudoku ever rated — up to the legendary monster puzzles.
- · Objective difficulty, measured by SE grade.
- · (soon) A precise skill rating — and who's truly the best.
- · Pick your exact difficulty, easiest to hardest.
- · Explaining hints — never auto-solves for you.
- · No mid-game ads.
How is difficulty measured?
SE grade is the difficulty number from Sudoku Explainer: the higher the grade, the more advanced the logic a puzzle demands. Easy puzzles sit near 1.0–2.0; the hardest monsters reach roughly 11.0 and above.
Read the full method on the SE grade page, or see the famous monsters on What is the hardest Sudoku?
Want to play one right now? Browse the full library on the puzzles by difficulty page.
Built for focus
Focus purely on the logic — we handle everything tedious for you.
Where this is going
Soon, you'll know your exact Sudoku skill as a number — and see who's truly the best.