Shudoku is sudoku, graded honestly. Most sudoku is graded by how many squares were blanked out, which tells you almost nothing. A 24-clue puzzle can fall over in two minutes; a 30-clue one can stop you dead. Here, every puzzle is solved the way a person solves it, and difficulty is measured by how hard it pushed back.
And the name? Shuzzles is Sh for Shaun and the rest for puzzles. Shudoku follows from there. The mark is an S drawn as a solve path through a grid, which is the thing this whole site is built to measure.
Every technique is written up here, each with a worked example taken from a real puzzle.
The hardest technique it needs
The solver works through the same repertoire you would — naked and hidden singles, locked candidates, naked and hidden subsets, X-Wing, Swordfish, Jellyfish, Y-Wing, XYZ-Wing, W-Wing, simple colouring, remote pairs, unique rectangles and BUG+1 — always reaching for the cheapest thing that works. If a puzzle cannot be finished without an X-Wing, it is not a Gentle, however few cells are blank. Technique sets a floor.
How much choice you get
This is the part clue counts miss. A puzzle where twenty cells are always available is a pleasant grind. A puzzle where at every turn there is exactly one cell in the whole grid you can fill is genuinely hard, even using nothing but singles. Those single-move states are pinch points, and we count them, along with the longest unbroken run of them and the average number of moves available per step.
| Band | Rating | Clues | Pinch points | Choices per step |
|---|---|---|---|---|
| Gentle | 40–50 | 32–37 | 0.0 | 10.9 |
| Moderate | 105–178 | 28–32 | 3.1 | 6.3 |
| Tough | 235–383 | 26–30 | 5.0 | 6.1 |
| Diabolical | 430–596 | 25–28 | 7.1 | 5.5 |
Notice that clue count barely separates Tough from Diabolical, while pinch points and available choices separate them cleanly. That is the whole argument.
No guessing, ever
A puzzle is only published if the solver finishes it without ever bifurcating. If a grid needs trial and error, it is thrown away, however nicely it grades otherwise.
Everything runs in your browser
This site is a set of static files. The solver that graded these puzzles is the same one that answers your hints, and it runs on your machine — so hints are instant, and the site keeps working with the network off.