How Does Stillgrid Grade Sudoku Difficulty, and What Is Evil Sudoku?

Stillgrid grades difficulty by the solving techniques a puzzle requires, not by how many cells start empty. Its hardest tier is labeled "Evil Sudoku," and the site also exposes a "Difficulty Grader" entry point alongside its variant and daily pages. The practical takeaway: pick a level by the techniques you're comfortable with, and treat "Evil" as the top of that technique ladder rather than a separate game mode.

Technique-based grading, in plain terms

Most casual players assume a puzzle with 50 blank cells is harder than one with 35. That's a weak proxy. A grid with many blanks can still fall apart under basic scanning, while a grid with fewer blanks can stall unless you know a specific advanced pattern.

Technique grading works the other way around: a solver (or a grading routine) attempts the puzzle using a fixed order of methods, from simple to advanced, and records the most demanding method needed to finish it. The tier is then assigned by that ceiling.

What this means for you

• Low tiers are solvable with basic scanning and simple elimination — good for warm-ups or learning.
• Middle tiers typically require intermediate patterns that reward practice but don't demand deep study.
• High tiers (including Evil) require advanced techniques; a wrong guess usually means a long, messy recovery.

The benefit is predictability. Two puzzles in the same tier should demand roughly the same kind of thinking, even if their blank-cell counts differ.

Where Evil Sudoku sits

Evil Sudoku is Stillgrid's top difficulty label — the tier reserved for puzzles that resist the simpler technique set. It is not a variant; it's a difficulty band that applies to the standard grid. If you're new to the site, start below it and move up only when the current tier feels routine rather than lucky.

A useful self-check: if you finish a puzzle and can't explain why each step was forced, you're probably one tier too high. Drop back, and the technique gap becomes visible.

The Difficulty Grader

Stillgrid lists a "Difficulty Grader" page among its tools. The intended use is straightforward: bring a puzzle you already have (from a book, a newspaper, or another site) and see which technique tier it lands in. That lets you calibrate outside puzzles against Stillgrid's own scale instead of guessing from appearance.

Because the site requires JavaScript to run its puzzles, expect the grader to work in-browser rather than as a downloadable file.

Choosing your level

Two habits make the ladder work better. First, finish a tier without pencil-mark clutter before moving up — speed isn't the signal, certainty is. Second, when you get stuck, note which technique you were missing; that's the actual next rung, not simply "a harder puzzle."

A quick example of why cell count misleads

Suppose you compare two puzzles: one with 40 blanks that collapses under basic scanning, and one with 30 blanks that stalls until you spot an advanced pattern. By blank count, the first looks harder. By technique grading, the second is the harder puzzle — and it's the one that will actually cost you time. That gap is exactly what technique-based tiers are designed to close.

Bottom line

Stillgrid's difficulty scale is about what you must know, not how empty the grid looks. Evil Sudoku is the top of that scale, the Difficulty Grader lets you map outside puzzles onto it, and the right level for you is the one you can finish with reasoning you can explain afterward.