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SeriesPuzzles

Sudoku

How Sudoku actually works — the rules, every solving technique in order of difficulty, and what to do when the grid stops moving.

49 parts12h totalSep 9, 2026 — Sep 9, 2026
Start part 1Read the overview →
  1. How to Play Sudoku: The Complete Rules for BeginnersOne rule: no digit repeats in a row, column or 3x3 box. Get the board named, the twenty peers explained, and the first four moves placed on a real grid.14 min
  2. Your First Sudoku, Solved One Move at a TimeOne 36-clue puzzle solved from the first empty cell to the last, with a checkable reason for all 45 digits and the two scans that find nearly every one.16 min
  3. Nine Beginner Mistakes That Make Sudoku Harder Than It IsScan by digit instead of by cell, use all three constraints, clear dead pencil marks, and stop guessing. Nine habits that make an easy grid feel hard, with the fix for each.16 min
  4. Sudoku Words: Cell, Box, Peer, Candidate, GivenCell, box, unit, given, candidate, peer, naked, hidden, pointing, fish. Every Sudoku word defined and shown on one worked grid, so the terms point at something.17 min
  5. Sudoku for Kids: Which Grid to Start On, and WhenStart a child on a 4x4, move to 6x6 once one is finished unaided, then the full grid. Two worked mini puzzles, three readiness tests, and the check that catches broken printables.13 min
  6. Sudoku for Seniors: Large Print and an Easier On-RampMeasure a cell before you trust the words large print, then start by hunting one digit at a time. A worked easy grid, print settings, phone versus tablet, and the brain evidence stated straight.15 min
  7. Every Sudoku Technique, Ordered From Easiest to HardestThe eight rungs in order, cross-hatching up to chains, each worked on a real grid: the cells the pattern clears, and how to tell when a puzzle needs the next one up.17 min
  8. Cross-Hatching: How to Read a Sudoku Grid QuicklyTake a digit, strike out the rows and columns that already hold it, and place the survivor. Cross-hatching worked digit by digit on one real grid until the puzzle falls.14 min
  9. Naked Singles and Hidden Singles, With Worked GridsA naked single is a cell with one candidate; a hidden single is a digit with one home in a unit. Both worked on real grids, including one with no naked singles at all.16 min
  10. How to Use Pencil Marks Without Drowning in ThemScan first, then mark. Full notation costs 70 digits on a stuck grid and Snyder costs 34, with one worked box showing what each finds and when to clear them.15 min
  11. Naked Pairs, Triples and Quads in SudokuTwo cells, two candidates, and the digits leave the rest of the unit. Naked pairs, triples and quads worked on real stuck grids, including the triple shape everyone walks past.13 min
  12. Hidden Pairs and Triples: Finding What Nobody Wrote DownTwo digits with the same two homes in a unit own those cells, whatever else is pencilled there. Two worked hard grids: a pair clearing eight candidates, a triple placing a digit.15 min
  13. Pointing Pairs and Box-Line Reduction, ExplainedPin a digit to one line inside a box and the rest of that line loses it. Two worked grids, the reverse move, and how to spot both from a cross-hatch with no pencil marks.15 min
  14. The X-Wing in Sudoku, Explained With Real GridsTwo rows where a digit fits in only two cells, both using the same two columns. The digit then leaves those columns everywhere else. Two worked grids that finish on singles after it.13 min
  15. Swordfish in Sudoku: The X-Wing With Three RowsThree rows that can only take a digit in the same three columns delete it from those columns everywhere else. Two real grids, the search filter, and the twin rule.14 min
  16. The XY-Wing, Explained SlowlyThree cells, two candidates each, and a digit that has to leave everything both wings can see. Two stalled hard grids worked from the bivalue list to the placement.16 min
  17. Advanced Sudoku Techniques for Extreme PuzzlesSingle-digit chains, the XYZ-Wing, the W-Wing and the unique rectangle, worked on three real extreme grids: the candidate each one kills, and what the grid does next.18 min
  18. How to Solve a Sudoku Without Ever GuessingA stalled grid means a missed move, a wrong digit or a broken puzzle. Two worked grids, the three symptoms of an early mistake, and what a guess costs on a real stall.14 min
  19. Stuck on a Sudoku? Work This Checklist in OrderStuck means a missed single, stale pencil marks, or a wrong digit written twenty moves back. Eight steps in order, worked on one real grid from a dead stop to a finished puzzle.17 min
  20. How to Use a Sudoku Hint Without Ruining the PuzzleRun the two-pass test, spend the check before the reveal, and take the smallest hint that moves you. Worked on a stalled grid where 11 of 29 reveals go nowhere.16 min
  21. Why Some Sudoku Puzzles Feel ImpossibleFour things make a Sudoku feel impossible and only one is the puzzle's fault. Tell them apart in two minutes, on a real 26-clue grid that stalls with 26 cells empty.15 min
  22. How a Sudoku Solver Works, and When You Should Use OneA solver returns the finished grid or nothing, and nothing means you went wrong. How backtracking works, counted on two real grids, and how to find your own mistake without reading the answer.16 min
  23. Scan a Sudoku With Your Phone Camera and Get the AnswerShoot the grid square on, crop to the border, then audit the digits before you solve. Includes the silent failure: one dropped given, twelve answers, and a tidy wrong grid.14 min
  24. Solving a Sudoku From a Photo: What Works, What FailsWhich images read cleanly and which fail, plus what each misread does: extra ink stops the solver dead, a dropped given hides, and one wrong digit moved 22 cells.14 min
  25. Solve Any Sudoku Step by Step, Using Only LogicThe order to work a grid in: scan by digit, re-scan after every placement, then mark one unit and cut. Worked on a 26-clue puzzle that stalls with 39 cells empty.16 min
  26. How to Write a Sudoku Solver: Backtracking, ExplainedThirty lines of Python that solve any 9x9 grid, a real trace of the search reversing out of a dead end, and the changes that cut 1,407 placements to 58.17 min
  27. How to Check a Newspaper Sudoku Answer Without Waiting a DayA finished Sudoku proves itself in about a minute: 27 groups, the printed clues, and no key. Two worked grids show the error rows catch and the one only boxes catch.15 min
  28. What Actually Makes a Sudoku Easy, Medium, Hard or ExtremeThe grade is the hardest technique a grid forces on you and how often, not the clue count. Two real puzzles settle it: 26 clues that fall to singles, 31 that need a chain.15 min
  29. How Long Should a Sudoku Take?Six minutes easy, twelve medium, twenty-two hard, thirty-five extreme. Why the clock grows nearly six times while the digits barely change, worked on two real grids.14 min
  30. Seventeen Clues: The Smallest Sudoku That Can ExistSeventeen givens is the proven floor and sixteen is impossible. A worked 17-clue grid that falls to singles alone, next to a 27-clue one that beats the whole toolkit.15 min
  31. Hard Sudoku: The Techniques That Actually Move the GridHard grids are a search problem, not a technique problem. Two real stalled puzzles, each opened by one elimination, and the order to work the moves in by price.13 min
  32. NYT Sudoku: How Easy, Medium and Hard Really CompareEasy needs only singles, Medium needs one pair, Hard needs an elimination that places no digit at all. Three worked grids show the exact move each label forces.13 min
  33. Newspaper Sudoku: USA Today, LA Times and the Washington PostA ninety-second sweep grades the grid better than the word above it. Two newspaper puzzles with 28 clues each: one falls to scanning, one makes you delete before you can write.16 min
  34. A Daily Sudoku Habit That Actually SticksPick the slot before the puzzle, run the same three-step opening every day, and treat the streak as a counter rather than the point. With a worked easy grid.15 min
  35. Types of Sudoku, From Classic to SamuraiClassic, Sudoku X, Jigsaw, Killer, Samurai and the odd grid sizes, each drawn as a region map, with the one move each type adds and the techniques that carry over unchanged.15 min
  36. Killer Sudoku: The Rules, and the Cage Sums Worth MemorisingThe one rule Killer adds to Sudoku, the sixteen cage sums with only one combination, and the 45 rule worked on a real grid until it hands you a digit for free.14 min
  37. Jigsaw Sudoku: When the Boxes Stop Being SquaresOne rule changes: the 3x3 boxes become nine irregular shapes. The rules, a worked 30-clue grid, and the law of leftovers that only an irregular layout can give you.14 min
  38. Samurai Sudoku: Five Grids, One PuzzleFive 9x9 grids in an X, four shared boxes, no new rule. The overlap move worked digit by digit, a real 98-clue samurai to solve, and its answer.13 min
  39. Sudoku X: What Two Diagonals ChangeThe one rule Sudoku X adds, the seventeen cells it touches, and three opening moves worked on a real diagonal grid that a classic solver cannot see.14 min
  40. 4x4, 6x6 and 16x16: Sudoku Beyond the Nine-by-NineBox shape, symbol set and peer count are all that change when a Sudoku grows. A worked 16x16 placement, the 6x6 rectangle trap, and why a 5x5 cannot exist.17 min
  41. Printable Sudoku: How to Print Them So They Are Actually UsablePrint at 100% with one puzzle per page and the cells come out big enough to write in. The dialog settings that decide cell size, how to judge a source, and a verified puzzle to test your printer.16 min
  42. Sudoku on Paper or on a Phone: An Honest ComparisonPaper keeps your marks and shows the whole grid; a phone makes a wrong digit cost nothing. A worked medium grid, the real pencil-mark cost of each, and how to buy a book.16 min
  43. Is Sudoku Good for Your Brain? What the Studies Actually FoundSudoku reliably makes you better at Sudoku. What the 19,000-person PROTECT study actually found, what it could not show, and how to solve so the effort counts.13 min
  44. Sudoku or Crosswords: Which One Should You Do?A Sudoku prints every constraint on the page; a crossword keeps half of them in your head. A worked grid, the brain evidence stated honestly, and how to run both.15 min
  45. Best Sudoku App: The Seven Tests to Run Before You Keep OneSeven tests you can run on any Sudoku app inside the first puzzle: notes, highlighting, wrong digits, the hard grade, flight mode, ad placement and resuming.17 min
  46. Offline Sudoku: Playing With No Signal and No AccountRun the flight-mode test before you need it: force-quit, reopen, play every grade. What offline has to cover, what an account buys, and where apps quietly fail.14 min
  47. Sudoku Apps and Ads: What to Look For Before You InstallWhere an ad lands matters more than how many there are. A worked grid showing what a full-screen ad costs you, the checks to run on a store listing, and the ten-minute test after.16 min
  48. The History of Sudoku: Number Place, Japan and a New ZealanderNumber Place ran in a Dell magazine in May 1979, Nikoli named it in 1984, and The Times printed one on 12 November 2004. Who did what, and how firm each attribution is.14 min
  49. What Does the Word Sudoku Actually Mean?Sudoku is Japanese for single numbers: 数 is number, 独 is single. The phrase Nikoli shortened, what the name forbids on a grid, and why the puzzle itself is American.11 min