Gameplay Settings are available on the main puzzle page.

• Use Normal Mode to enter numbers you are confident or sure about. 
• Use Candidate Mode to add or remove multiple possibilities for a square.
• You can also toggle between Candidate and Normal mode by selecting these options at the bottom of the puzzle in the Games app or pressing spacebar on the website. Holding Shift will also toggle between modes until you release.
• Auto-Candidate Mode automatically fills the board with all eligible candidates within each cell. Entering a number in Normal Mode will also eliminate relevant candidates in that cell's row and column.
• Use the Undo button to undo your last action, including entering and deleting both candidates and normal entries.
• Use the X button to clear a cell of all normal entries and candidates.

Gameboard Settings are found by selecting the gear icon in the top right corner of the app or website.

• Dark and Light Mode (app only) - Dark Mode allows you to change the display of The New York Times app to a light-on-dark color scheme, while Light Mode changes the display to a dark-on-light color scheme.
  • The app will respect your device's preferred display settings by default.
• Check guesses when entered - Upon entering a number into a cell in normal mode, correct guesses will be highlighted in blue and incorrect guesses will be marked with a red dot.
• Show error counter - The error counter keeps a running tally of the number of errors made throughout the course of playing the puzzle.
• Highlighting - Highlighting the box allows you to see more clearly the cell or box that you have currently selected. Other options include highlighting the rows, columns, and any identical numbers throughout the rest of the puzzle that correspond to the box you have currently selected.
• Play Sound on Solve - The app or website will play a jingle after the puzzle is completed successfully.

Sudoku uses different colors and symbols to show whether your entries are correct, unchecked, or contain an error.

• Blue numbers indicate entries that have been checked and confirmed as correct.
• Black numbers are entries that have not yet been checked.
• A red dot in the corner of a cell shows there is a conflict in that square.
• A red slash across a number indicates that entry is incorrect.

If you are new to Sudoku or looking to improve your solving efficiency, you can explore our step-by-step guide on how to solve Sudoku at nytimes.com. For more advanced strategies and techniques, you may also find resources like these advanced Sudoku strategies helpful.

If you are concerned there may be an error in a Sudoku puzzle, select the ellipsis (…) in the top-right corner of the game and select Check Puzzle to see if any numbers are out of place. If there are no red slashes indicating an error but the puzzle still will not complete, please use Report a bug in the Games app or Contact Us from the Games webpage so our team can investigate.

To share comments or suggestions about Sudoku, submit feedback directly from within the game by following these steps:

1. Navigate to Sudoku in the New York Times Games app or on the website.
2. Select the Question Mark icon in the upper right corner of the game.
3. Select Feedback.
4. Fill out the form and submit it.