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Data report

What each Sudoku difficulty level asks of you

We solved all 60,000 puzzles in our Sudoku app with the app's own hint engine and recorded the hardest technique it used on each one. That technique, not the number of clues, is what sets a level.

Updated 2026-10-05

60,000puzzles analyzed
29techniques are the hardest step in at least one puzzle
26starting clues in a typical Expert, Master or Extreme puzzle

Five things the numbers show

  1. Clues do not set the level. Expert, Master and Extreme puzzles start from the same setting (26 to 30 clues, usually 26), yet each level is decided by its own family of techniques.
  2. Medium is one skill. All 10,000 Medium puzzles are decided by a Hidden Single; our engine never needed anything harder for them.
  3. Hard is about where rows, columns and boxes cross. The Pointing Pair, the Pointing Triple and the Box/Line Reduction decide 74.9% of Hard puzzles; pairs and triples decide the rest.
  4. The famous X-Wing is rarely needed. Our engine used it in only 6.3% of Expert puzzles and it was the hardest step in 3.7%, while the Skyscraper was the hardest step in 55.1% and the Y-Wing in 30.3%.
  5. Extreme mostly means one pattern: ALS-XZ decides 86.3% of Extreme puzzles, and the Unique Rectangle decides most of the rest (12.1%).

The deciding technique, level by level

Each bar is the share of that level's puzzles whose hardest step, as our engine solved them, is this technique. All six charts use the same scale, from 0 to 100%.

Easy

10,000 puzzles, 51 clues to start
  1. Nearly Complete95.1%
  2. Naked Single4.9%

Medium

10,000 puzzles, 36 clues to start
  1. Hidden Single100%

Hard

10,000 puzzles, 31 clues to start
  1. Pointing Pair59.6%
  2. Naked Pair18.3%
  3. Box/Line Reduction13.1%
  4. Hidden Pair6.0%
  5. Pointing Triple2.2%
  6. Naked Triple0.8%
  7. Hidden Triple0.1%

Expert

11,034 puzzles, 26 to 30 clues to start
  1. Skyscraper55.1%
  2. Y-Wing30.3%
  3. Empty Rectangle5.9%
  4. Simple Coloring4.4%
  5. X-Wing3.7%
  6. Swordfish0.5%
  7. Naked Quadunder 0.1%

Master

9,590 puzzles, 26 to 30 clues to start
  1. XY-Chain59.3%
  2. W-Wing28.1%
  3. X-Chain6.1%
  4. XYZ-Wing5.0%
  5. Grouped Two-String Kite0.9%
  6. Two-String Kite0.4%
  7. WXYZ-Wingunder 0.1%

Extreme

9,376 puzzles, 26 to 30 clues to start
  1. ALS-XZ86.3%
  2. Unique Rectangle12.1%
  3. Finned X-Wing1.2%
  4. Finned Swordfish0.4%
  5. ALS-XY-Wingunder 0.1%
Show the numbers as a table

Hardest step in: the share of the level's puzzles where this was the hardest technique the engine used. Used in: the share where the engine used it at least once.

LevelTechniqueHardest step inUsed in
EasyNearly Complete95.1%100%
EasyNaked Single4.9%4.9%
EasyLast Remaining Cell0.0%100%
MediumHidden Single100%100%
MediumNearly Complete0.0%100%
MediumLast Remaining Cell0.0%100%
MediumNaked Single0.0%99.5%
HardPointing Pair59.6%66.6%
HardNaked Pair18.3%19.1%
HardBox/Line Reduction13.1%14.4%
HardHidden Pair6.0%6.0%
HardPointing Triple2.2%2.6%
HardNaked Triple0.8%0.8%
HardHidden Triple0.1%0.1%
HardNearly Complete0.0%100%
HardLast Remaining Cell0.0%100%
HardHidden Single0.0%99.9%
HardNaked Single0.0%97.9%
ExpertSkyscraper55.1%56.4%
ExpertY-Wing30.3%36.4%
ExpertEmpty Rectangle5.9%5.9%
ExpertSimple Coloring4.4%4.6%
ExpertX-Wing3.7%6.3%
ExpertSwordfish0.5%0.9%
ExpertNaked Quadunder 0.1%under 0.1%
ExpertNearly Complete0.0%100%
ExpertLast Remaining Cell0.0%100%
ExpertHidden Single0.0%100.0%
ExpertNaked Single0.0%97.7%
ExpertPointing Pair0.0%22.7%
ExpertNaked Pair0.0%13.3%
ExpertHidden Pair0.0%6.5%
ExpertBox/Line Reduction0.0%5.5%
ExpertPointing Triple0.0%1.3%
ExpertNaked Triple0.0%0.9%
ExpertHidden Triple0.0%0.3%
MasterXY-Chain59.3%59.4%
MasterW-Wing28.1%34.0%
MasterX-Chain6.1%7.3%
MasterXYZ-Wing5.0%6.8%
MasterGrouped Two-String Kite0.9%1.0%
MasterTwo-String Kite0.4%0.5%
MasterWXYZ-Wingunder 0.1%under 0.1%
MasterNearly Complete0.0%100%
MasterLast Remaining Cell0.0%100%
MasterHidden Single0.0%100.0%
MasterNaked Single0.0%98.4%
MasterPointing Pair0.0%25.8%
MasterNaked Pair0.0%14.1%
MasterSkyscraper0.0%12.1%
MasterY-Wing0.0%12.0%
MasterHidden Pair0.0%7.5%
MasterBox/Line Reduction0.0%5.8%
MasterX-Wing0.0%3.0%
MasterEmpty Rectangle0.0%2.0%
MasterSimple Coloring0.0%1.8%
MasterPointing Triple0.0%1.5%
MasterNaked Triple0.0%1.4%
MasterSwordfish0.0%0.3%
MasterHidden Triple0.0%0.3%
MasterNaked Quad0.0%under 0.1%
MasterHidden Quad0.0%under 0.1%
ExtremeALS-XZ86.3%86.3%
ExtremeUnique Rectangle12.1%17.3%
ExtremeFinned X-Wing1.2%1.4%
ExtremeFinned Swordfish0.4%0.6%
ExtremeALS-XY-Wingunder 0.1%under 0.1%
ExtremeHidden Single0.0%100%
ExtremeNearly Complete0.0%100%
ExtremeLast Remaining Cell0.0%100%
ExtremeNaked Single0.0%98.3%
ExtremePointing Pair0.0%29.4%
ExtremeXY-Chain0.0%18.7%
ExtremeNaked Pair0.0%16.7%
ExtremeSkyscraper0.0%11.8%
ExtremeY-Wing0.0%11.0%
ExtremeHidden Pair0.0%9.5%
ExtremeW-Wing0.0%7.9%
ExtremeBox/Line Reduction0.0%7.6%
ExtremeX-Wing0.0%3.7%
ExtremeEmpty Rectangle0.0%2.5%
ExtremeX-Chain0.0%2.1%
ExtremeNaked Triple0.0%1.8%
ExtremeXYZ-Wing0.0%1.8%
ExtremeSimple Coloring0.0%1.6%
ExtremePointing Triple0.0%1.5%
ExtremeSwordfish0.0%0.6%
ExtremeHidden Triple0.0%0.5%
ExtremeGrouped Two-String Kite0.0%0.2%
ExtremeWXYZ-Wing0.0%0.1%
ExtremeTwo-String Kite0.0%0.1%
ExtremeNaked Quad0.0%under 0.1%

Download the data (CSV)

How we measured it

  • The puzzles: all 60,000 puzzles that ship in the Sudoku app by Rubigo Games (puzzle bank version 3, generated on 2026-03-30).
  • The solver: the app's hint engine fills one cell at a time. At every step it takes the first technique on its fixed ladder, from easiest to hardest, that places a digit. The hardest technique it used along the way is the puzzle's deciding technique, and that technique's level is the puzzle's level.
  • Clues are a generator setting: Easy puzzles start with 51 clues, Medium with 36 and Hard with 31. Expert, Master and Extreme come from one setting (26 to 30 clues) and are sorted only by the technique they need.
  • What is left out: a puzzle the engine could not finish with a named technique was not kept, so every puzzle counted here was solved with the techniques shown, without guessing.
  • One route, not the only one: the engine always takes the easiest step that places a digit, and it does not carry notes from one step to the next. A player who keeps notes may get through some puzzles with easier techniques.
  • Checked again on 2026-10-05: we re-solved every puzzle with the current engine, and all 60,000 landed on the same level they have in the app.
  • Other apps grade differently, so these shares describe the puzzles in our app, not every Sudoku ever made.

Use the data

The numbers on this page are free to reuse under CC BY 4.0. Please link to this page as the source.

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