Difficulty, Daily Challenge and Stats
How the five difficulties differ, how the daily challenge is scheduled, and how streaks and best times are counted.
Difficulty is about technique
Many sudoku sites grade puzzles by how many numbers are given, but fewer numbers does not mean harder: some puzzles give only 22 numbers and still fall to singles alone. Here, a solver works through each puzzle the way a person would, always trying the simplest technique first. The hardest technique the puzzle needs is its difficulty.
| Difficulty | Techniques needed | Given numbers |
|---|---|---|
| Easy | hidden single and naked single | 38–44 |
| Medium | Same as Easy | 30–34 |
| Hard | + pointing pair, box/line reduction, naked pair, and hidden pair | As few as possible |
| Expert | + naked triple, hidden triple, X-Wing, and XY-Wing | As few as possible |
| Evil | + Swordfish and XYZ-Wing | As few as possible |
Easy and Medium use the same techniques; the difference is how many numbers are given. With fewer numbers, the singles are better hidden. From Hard upward, numbers are removed until no more can go: take away one more and the puzzle would have more than one solution.
Every puzzle passes two checks after it is generated: it has exactly one solution, and these techniques can solve it from start to finish. So no puzzle ever needs a guess. If you are stuck, there is a step you have not seen yet.
Daily challenge
There is a new puzzle every day, the same for everyone, and it changes at midnight in your time zone. The difficulty follows the day of the week, easiest on Monday and hardest at the weekend:
| Day | Difficulty |
|---|---|
| Monday | Easy |
| Tuesday | Medium |
| Wednesday | Medium |
| Thursday | Hard |
| Friday | Hard |
| Saturday | Expert |
| Sunday | Expert |
- Press "Play today" on the daily challenge card in the menu to start.
- Pick any past day on the calendar to play it later; days you have solved are marked.
- Your streak only counts puzzles solved on their own day: solve today's puzzle today and your streak grows by one. Catching up on past puzzles does not repair a broken streak.
Stats
"Your stats" at the bottom of the menu is kept separately for each difficulty:
| Item | How it is counted |
|---|---|
| Played | Games that ended in a win or after too many mistakes (abandoned games do not count) |
| Win rate | Games won ÷ games played |
| Best time | Your fastest qualifying win (see below) |
| Average | The average time of all wins |
| Best streak | Your most wins in a row at this difficulty |
Best time leaves out two kinds of wins: games where you used a hint, and games you kept playing with a second chance after 3 mistakes. Auto notes do not count as a hint, so use them freely.
Stats and saved games live in this browser only. There is no sign-up and nothing is uploaded. On another device, or after clearing your browser data, your records will not be there.
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