Sudoku guides
- How to play Sudoku — Learn Sudoku by solving a real Easy puzzle step by step: what to scan first, how to place a digit with confidence, and when taking a hint beats a guess.
- How to solve Sudoku — The complete Sudoku method from singles to unique rectangles, with a worked Medium example, a table of what to look for and links to all twelve lessons.
- How to use pencil marks — How to use pencil marks in Sudoku: when to start, full versus selective marking, what Auto-notes does, and habits that keep your candidate notes accurate.
- Sudoku strategy by difficulty — What to learn at each Sudoku level, Easy to Evil: the techniques each one adds, which to practice first, and how often each appears in the site's puzzles.
- Common Sudoku mistakes — The common Sudoku mistakes sorted into groups: guessing, misreading the board, stale pencil marks and misapplied techniques, with ways to catch and undo them.
- How Sudoku difficulty is graded — How this site grades Sudoku difficulty by technique, not clue count: the solver, the five tiers, how puzzles earn a level and what grading cannot measure.
- How puzzles are generated and verified unique — How the site's Sudoku puzzles are generated and checked: random grids, clue removal, a solution counter that stops at two, and a check on every stored puzzle.
- Technique frequency by difficulty — Which techniques each Sudoku level needs, counted over 1,000 stored classic puzzles per level, with the method, sample sizes and what the numbers don't show.
- Build a Sudoku solver in TypeScript — Build a Sudoku solver in TypeScript: backtracking search, a solution counter that proves uniqueness and a clue-removal routine, with tests you can run.
- Sudoku on mobile — Sudoku on a phone: digit-first entry, notes, large digits and a left-handed pad, auto-pause, what is saved on your device and what to do if something fails.
The ten guides here cover how to play and solve Sudoku, how to use this game’s tools, and how the site itself works. Start with how to play for a narrated first puzzle, or with how to solve Sudoku for the complete method.
The data and process guides show how puzzles are generated, verified and graded, and one tutorial builds a working solver in TypeScript.
Where should you start?
Pick the guide that matches where you are. If you have never finished a puzzle, read how to play Sudoku, which solves the first moves of a real Easy puzzle and explains each deduction. If you can finish Easy and want to move up, read how to solve Sudoku, the longest guide, which climbs from singles to unique rectangles and links all twelve technique lessons.
Learning to solve
- How to play Sudoku is a guided first puzzle with the reasoning for every move.
- How to solve Sudoku is the full solving method, rung by rung, with a worked example from a Medium puzzle.
- Sudoku strategy by difficulty says what to learn at each of the five levels and which technique to practice first.
- Common Sudoku mistakes sorts the usual errors into groups and shows how to catch and undo them.
Using the game well
- How to use pencil marks explains when to write candidates, how Auto-notes behaves and which habits keep notes accurate.
- Sudoku on mobile covers touch entry, digit-first mode, the settings that help on a small screen and what to do when the game pauses.
The controls page is the reference for every key, button and setting, and the rules page covers the rules of every board.
How the site works
These three guides are about the puzzles themselves and are meant to be checkable.
- How Sudoku difficulty is graded explains the technique-based grading, its method and its limits. It is this site’s own system and not an industry standard.
- How puzzles are generated and verified unique describes the generator, the solution counter and the check that is repeated for every stored puzzle.
- Technique frequency by difficulty is a data page computed by a script from the stored puzzles, with the sample sizes and method shown.
For programmers
Build a Sudoku solver in TypeScript is a step-by-step tutorial. It builds a backtracking solver, a solution counter that proves uniqueness and a clue-removal routine, with tests you can run.
How are the guides kept honest?
Every number in these guides comes from a script in the site’s repository or from the site’s own data files, and each guide says which. Walkthroughs use real stored puzzles, and the solver tutorial’s code was run and tested before it was published. Where a limit applies, such as the grading being the site’s own method, the guide says so.
Suggested reading orders
- Beginner: how to play, then pencil marks, then common mistakes.
- Improver: strategy by difficulty, then how to solve, then the lessons in the techniques hub that match your level.
- Curious about the site: difficulty grading, then generation and verification, then technique frequency.
- Developer: generation and verification, then the TypeScript solver tutorial.
Whichever you choose, you can put it into practice straight away on the home page, or look through the boards on the games hub. Terms you are unsure of are in the glossary.