Expert mode Sudoku

It uses the same rules as the home page and is meant for players who can already finish Expert puzzles with checking of their own.

What is taken away?

The board is the classic 9×9 grid with the usual rules, set out on the rules page. What changes is the support around it:

• No hints. The Hint button and the H key are not available.
• No auto-notes. You can still write pencil marks with the Notes button, but you fill and maintain them yourself.
• No mistake feedback. The game does not flag conflicts or wrong digits, and there is no Check button.
• No restart or new puzzle. The New and Restart buttons are removed, and the level chooser is locked while a puzzle is in progress.
• One attempt. When the grid is full and not correct, the game ends the attempt and records a loss.

Undo, redo, erase, pause and the display settings all still work. The controls page lists which buttons appear.

Which puzzles does it use?

The mode has its own pool of 60 Expert and 60 Evil puzzles, each verified to have exactly one solution, with between 23 and 29 givens. You choose between the two levels. From the pool’s technique data:

• Expert: XY-Wing in 58% of puzzles and simple coloring in 52%, with pointing pairs in 75% and naked pairs in 40%.
• Evil: every puzzle needs a unique rectangle, and pointing pairs appear in 93%, box/line reduction in 70% and naked pairs in 67%.

With 60 puzzles per level the percentages are approximate. The larger classic pool in the frequency guide shows the same general shape. Because the puzzles come from the same grading as the home page, an Expert puzzle here is as hard as an Expert puzzle there. What makes this mode harder is the absence of help, and not the puzzles.

How should you prepare?

1. Be fluent in the techniques first. At Expert, XY-Wing and simple coloring carry most puzzles. At Evil you also need unique rectangles. With no hint available, you must find them yourself.
2. Practice with feedback first. Solve Expert and Evil puzzles on the home page with mistake feedback on, and then switch it off to see how you fare.
3. Build your notes by hand. Decide in advance whether you will mark every cell or only some. The pencil marks guide describes both styles.
4. Read the strategy guide. Strategy by difficulty says what each level asks for.

How do you avoid a wrong grid?

With feedback off and one attempt, the last moves are the dangerous ones. A single wrong digit placed early can survive almost to the end. Some routines help.

• Verify every house before the final digit. Run through each row, column and box and confirm it holds each digit once. Fill the last cell only when everything else checks.
• Be careful with unique rectangles. The shortcut relies on the puzzle having exactly one solution, which these puzzles do, but a misread rectangle gives a wrong elimination. Count the corners and boxes twice.
• Keep notes honest. A stale note can invent a pattern. When a big deduction depends on several marks, re-check them against the board.
• Use undo, not erase, when you doubt a move. Undo restores values and notes together.

The common mistakes guide sorts the usual errors and shows how to trace a late contradiction back to its source.

What happens to the result?

Your result, win or loss, is recorded in this browser’s statistics for the mode. The game pauses when you switch away and keeps the board in your browser, so an interruption does not by itself end the attempt or record a loss. Statistics stay on your device and are not shared.

Where does it sit among the boards?

It is the strictest board. For the same Expert and Evil puzzles with help, choose a level on the home page. For a shared puzzle that changes with the day, try daily Sudoku. If you want a new kind of reasoning at the same difficulty, look at killer or irregular. The games hub lists every board.