Which Sudoku Technique for Each Level?

Overview

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.

To find out the level of a specific puzzle, enter it in the solver: it rates it on this scale and shows every technique used, step by step.

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.

Puzzles verified automatically

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.

Validation scan of Evil puzzles: 31 puzzles analyzed, 31/31 solved, 31/31 unique solution, 31/31 level compliant — 31/31 puzzles compliant with the Evil level

Detail of Evil-level puzzles, all compliant with a unique solution and the techniques used listed — Per-puzzle detail — techniques used for each

Easy

Direct scanning, a single technique

Pencil notes: not needed

The Easy level only requires a single technique, applied by scanning the grid with your eyes: no notes to take.

Hidden Single Learn more → For a given number, only one cell remains possible in a unit (block, row or column): you place it directly.

Medium

One step further, notes recommended

Pencil notes: not required, but often recommended

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.

All Easy-level techniques
Locked Candidates (Pointing and Claiming) Learn more → A number confined to a block within a single row/column gets eliminated from the rest of that row/column, and vice versa.

Hard

Time to pick up the pencil

Pencil notes: required (Phase 2)

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.

All Easy and Medium-level techniques
Naked Single Learn more → A cell has only one noted candidate left: that's the answer.
Naked Twins / Triples / Quads Learn more → N cells in a unit collectively contain only N candidates: those numbers are eliminated from the other cells.
Isolated groups (N=4 generalization) Learn more → The same logic as twins/triples, extended up to 4 cells.
Hidden Pairs / Triples Learn more → N numbers only appear as candidates in N cells of a unit: all their other candidates are eliminated.
Mixed groups (generalized Hidden Subsets) Learn more → An extended version of hidden pairs/triples, up to 4 numbers confined to 4 cells.

Expert

Local patterns

Pencil notes: required

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.

All techniques from the previous levels
X-Wing Learn more → A candidate aligned in a rectangle across 2 rows × 2 columns: it's eliminated from the rest of those columns (or rows).
Skyscraper Learn more → An "asymmetric" X-Wing with 4 cells, sharing only a single column (or row).
Swordfish Learn more → The extension of the X-Wing to 3 rows × 3 columns.
XY-Wing Learn more → A pivot cell with 2 candidates and two branches that let you eliminate a shared candidate elsewhere.

Evil

Chains and coloring

Pencil notes: required

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".

All techniques from the previous levels
Simple Coloring Learn more → You alternately "color" cells linked by strong links to deduce a value by contradiction or convergence.
XY-Chains Learn more → The extension of the XY-Wing to a chain of arbitrary length.
X-Chains Learn more → A chain of alternating deductions (strong/weak links) involving a single candidate number.

These techniques build on the Expert-level patterns covered earlier, including X-Wing — read the X-Wing technique in detail on the blog.

Put it into practice

Ready to test your level on a real puzzle?

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