Sudoku-Land offers five difficulty levels: Easy, Medium, Hard, Expert and Evil. Each level maps to a precise set of solving techniques — the higher the level, the more demanding the techniques required, on top of everything from the levels below.
This page simply answers the question "which technique do I need to master for this level?". For a detailed explanation of each technique (principle, example, tip), head over to the How to Play page.
| Level | Key techniques | Pencil notes |
|---|---|---|
| Easy | Hidden Single | Not needed |
| Medium | + Locked Candidates | Recommended |
| Hard | + Naked Single, Twins/Triples/Quads (naked and hidden) | Required |
| Expert | + X-Wing, Skyscraper, Swordfish, XY-Wing | Required |
| Evil | + Simple Coloring, XY-Chains, X-Chains | Required |
General rule: a puzzle at a given level always solves by first exhausting the techniques from the levels below it. Pencil notes (candidates) become essential from the Hard level on, but they're already often useful as early as Medium.
Every puzzle offered on Sudoku-Land goes through an internal validation tool that solves it with a solver reproducing the human solving techniques listed on this page (no brute force) — this confirms both that the puzzle has a genuine unique solution and that its announced level truly matches the techniques required to solve it. Example below: a full scan of the 31 puzzles offered during a given month for the Evil level.
The Easy level only requires a single technique, applied by scanning the grid with your eyes: no notes to take.
In theory you're still working by direct scanning, but you now also look for candidates confined to a block or a row/column — a pattern that quickly gets hard to track by eye on a busy grid. In many cases, jotting down candidates helps you avoid mistakes: notes aren't strictly required at this level, but they're strongly recommended.
From this level on, direct scanning is no longer enough: you need to note all candidates in every empty cell. Four technique families grouped into a single tier.
Four techniques that rely on a pattern to spot visually in the grid (a rectangle, a wing), without having to follow a chain of deductions across the whole grid.
The most demanding level: these three techniques require building and following a chain of deductions across the whole grid — a different mental exercise from the local patterns of the Expert level, not just "one notch harder".