The Problem with Sudoku Difficulty Labels

Every day, millions of sudoku players download puzzles from various websites and apps, trusting that an "Expert" puzzle is genuinely expert-level. But what does "Expert" actually mean? One site's "Hard" might be another's "Medium." This inconsistency frustrates players who use difficulty labels to find appropriately challenging puzzles.

To address this, I conducted a comprehensive audit: solving 30 expert-difficulty sudoku puzzles from 10 different generators and websites, meticulously tracking solving time, required techniques, and comparing each puzzle's labeled difficulty against its actual complexity.

Methodology

Over the course of three weeks, I solved three expert-difficulty puzzles from each of these 10 sources:

• Site A: WebSudoku.com
• Site B: Sudoku.org
• Site C: KrazyDad Sudoku
• Site D: Sudoku Kingdom
• Site E: Sudoku-Online.com
• Site F: Puzzle.com Sudoku
• Site G: SudokuSnake
• Site H: Sudoku-Puzzles.net
• Site I: DailySudoku.com
• Site J: Simon Tatham's Portable Puzzle Collection