Why practise by technique instead of by difficulty
Ask two publishers what “hard” means and you will get two different answers. One grades by how long a test panel took, another by how many clues it withheld, a third by whatever its generator happened to output. The result is familiar to every solver: you finish a “fiendish” puzzle over coffee, then stall completely on a “medium” from a different app.
What actually makes a puzzle hard is far more specific — it is the hardest named pattern you must find in order to make progress. A puzzle that needs nothing beyond singles is easy for anyone fluent in singles. A puzzle that cannot be finished without an X-Wing is hard for everyone who has never trained one, and unremarkable for everyone who has. In other words, a “hard” puzzle is simply a puzzle that requires a technique you have not internalised yet. That is not a verdict on your intelligence; it is a to-do item.
Which is the whole argument for technique-first practice. Pattern recognition is built by repeated, labelled exposure with immediate feedback — the same way a chess player drills tactical motifs rather than playing random games and hoping a fork turns up. If you want to learn to see Hidden Pairs, the efficient path is twenty puzzles that all contain Hidden Pairs, not two hundred puzzles that might. The technique picker exists to make that possible, and the learning-order guide lays out the sequence worth following.
How to play
The board here is elimination-first, which makes it behave a little differently from most Sudoku apps and is worth thirty seconds of explanation:
- Select a number from 1–9 at the bottom of the screen.
- Tap a cell to eliminate that number as a candidate there.
- When only one candidate remains in a cell, it resolves to that digit automatically. This is irreversible by design — it removes any temptation to guess and check.
- Alternatively, long-press a cell for one second to eliminate every candidate except the selected one, solving the cell immediately.
The reason for the inversion is that elimination is the reasoning. Typing a digit into a cell records a conclusion and throws away the argument that produced it; removing a candidate records the argument itself. Solve this way for a week and the techniques below stop being things you look up and start being things you notice. The pencil-marks guide covers how to keep candidate notation from becoming a chore.
The technique ladder
These are the eleven named patterns the site teaches, roughly in the order worth learning them. Each links to an interactive lesson with a live demo, spotting advice, and common mistakes; each also has worked walkthroughs on real boards and curated practice puzzles.
| Technique | What it is |
|---|---|
| Naked Single | A cell has exactly one candidate left. The foundation every other technique cashes out into. |
| Hidden Single | A digit fits only one cell in a row, column, or box — even though that cell has other candidates. |
| Naked Pair | Two cells in a unit hold the same two candidates, locking both digits out of the rest of the unit. |
| Omission | A box confines a digit to one row or column, so it can be eliminated along the rest of that line. |
| Naked Triplet | Three cells share three candidates between them, clearing those digits from the unit. |
| Hidden Pair | Two digits appear in only two cells of a unit, so every other candidate in that pair falls away. |
| Hidden Triplet | Three digits are confined to three cells, stripping all other candidates from them. |
| Naked Quad | Four cells holding only four candidates between them lock those digits in place. |
| Hidden Quad | Four digits restricted to four cells, clearing everything else out of those cells. |
| X-Wing | A candidate pinned to the same two columns in two rows forms a rectangle you can eliminate around. |
| Swordfish | The three-row, three-column version of the X-Wing — the first genuinely hard pattern. |
A useful rule of thumb: the first two will carry you through the large majority of newspaper puzzles, the next five cover almost everything a “hard” rating throws at you, and the last two are where Sudoku stops being arithmetic bookkeeping and starts being genuinely interesting.
Where to start
If you are new to Sudoku: read scanning techniques first, then drill Naked Singles and Hidden Singles until you can clear an easy grid without pencil marks at all. Do not move on early; fluency in singles is what makes every later technique cheap to spot.
If you solve comfortably but stall on hard puzzles: your missing rung is almost certainly subsets or locked candidates. Work Omission, then Naked Pairs and Hidden Pairs, and read why subsets work so the pattern is a piece of reasoning rather than a shape you memorised.
If you already know the subsets: go to X-Wing and Swordfish, read fish patterns explained to see why they are one idea at two sizes, then test yourself on the technique combinations and the hardest puzzles in the library.
Frequently asked questions
- Is Precision Sudoku free?
- Yes. Every puzzle, lesson, walkthrough, and printable sheet on the site is free, with no account to create and nothing to buy. The site is supported by advertising.
- What makes this different from other Sudoku sites?
- Most sites label puzzles easy, medium, or hard. Those labels are not comparable between publishers and they tell you nothing about what you will actually have to do. Precision Sudoku labels puzzles by the solving techniques they require, verified by a step-by-step logical solver, so you can practise one named pattern at a time.
- Do I need to know the advanced techniques to start?
- No. Naked Singles and Hidden Singles alone will finish a large share of newspaper puzzles. Work down the technique ladder only when a puzzle stalls on you — that stall is the signal you are ready for the next pattern.
- Why does the board make me eliminate candidates instead of typing answers?
- Because elimination is what solving actually consists of. Typing a digit records a conclusion; removing a candidate records the reasoning that produced it. A cell resolves automatically once one candidate remains, so the answer arrives as a consequence of the logic rather than as a guess you check afterwards.
- Can I print these puzzles?
- Yes. The printable section offers easy through expert sheets with answer keys on a separate page, laid out for a clean single-sheet print with no ink-heavy backgrounds.
- Does every puzzle have exactly one solution?
- Yes. Every puzzle in the library is verified unique by the solver before it is published, so no puzzle ever requires guessing between two valid completions.
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