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Email support@johncotter.io with your device model, operating-system version, app version, and what happened. Screenshots are optional. Please do not send passwords or unrelated personal information.

Classic Sudoku

Choose Easy, Medium or Hard. In version 1.1, Number first is the default: select a number, then tap squares to place it. Choosing another number does not edit your last square. Settings also offers Square first: select a square, then enter a number; choose the next square before writing again. Original clues cannot be changed. Erase follows your chosen input style. Warm-colored numbers and small dots indicate repeated digits in a row, column or box; they do not compare your entry with a hidden answer. Each classic puzzle has one solution; difficulty labels describe clue removal rather than a human-solving strategy rating.

Pencil marks

Turn on Pencil to add or remove possible numbers in empty squares. In Square first mode the square stays selected so you can enter several notes. Fill notes calculates candidates allowed by the current board. Writing a number clears the square's notes and removes that number from peer notes. Undo restores recent edits while the game remains open; undo history is not kept after a restart.

Sudoku Exchange

The board starts full and every row already contains 1 through 9. Tap two numbers in the same row to swap them. Repair repeated digits in the columns and boxes; any valid completed Sudoku wins. The board shows conflict dots and remaining column and box counts. Gold and silver thresholds use a known repair route, not a claim of the shortest possible solution. Bronze is awarded for finishing. Undo restores a swap but does not refund its move count.

Daily puzzles and your journal

The daily Exchange is the same versioned puzzle for everyone on a given UTC date and works offline. Replaying a completed daily is labeled as a replay; its time does not replace a first-solve personal best. The journal records completed games, times, Exchange moves and medals. Best times are separate by mode and difficulty.

Daily streak and rest days

Solving the daily Exchange builds a streak of consecutive UTC days. The count is worked out from your journal rather than stored separately, so it always agrees with your record. A run survives to the end of the next UTC day. Every seventh solved day earns a rest day, held at most two at a time; a rest day covers one missed day, so a single busy day does not erase weeks. Rest days belong to the run that earned them, and a broken run starts again with none. Replaying a daily you have already solved does not extend a streak. The home screen shows your run, the next named milestone and what today is worth before you play. The journal shows current and longest runs, days played, daily medals and a 28-day ribbon. Nothing you have earned is lost when a run ends; there is no currency, only the count.

Daily reminder

An optional daily reminder is off by default. Turning it on is the only thing that asks your device for notification permission, and declining leaves it off with a route to system settings. Reminders are local to your device: no account, no push token, no remote delivery and no new information leaving the device. They are silent, arrive at most twice in a day, and are never scheduled for a day you have already solved. One arrives at the local hour you choose; a second, last call arrives an hour before midnight UTC only when a run of three days or more is still unplayed. Reminders work in the installed app and are not available in the web version; a device that cannot schedule them keeps every other part of the game working.

Settings and time

Choose Signal, Blueprint or Print, optional offline ambient music and its volume, gentle haptics, the daily reminder and its time, input style, conflict highlighting and timer visibility. Music is off initially and pauses outside the app. The timer measures active play and pauses when you leave the game, put the app in the background or press Pause. Manual pause hides the puzzle. Hiding the timer only hides its display; time still saves to your journal.

Progress and connectivity

Version 1.1 and later save one current game, pencil marks, preferences and your completed-game journal locally between launches. Continue puzzle resumes your game. Starting another puzzle asks before replacing unfinished progress. Earlier versions did not save between launches. Clearing storage or uninstalling removes local saves, subject to separate operating-system backup behavior; we cannot recover lost data. Gameplay and music work offline. Advertising and privacy forms require a connection; missing ads do not remove game features.

Advertising choices

The app requests non-personalized, general-audience ads and applies under-age-of-consent treatment to everyone without collecting or verifying an age. When required by Google, use Ad privacy options below the game to review choices. You never need to click an ad to play.

Privacy requests

Email contact@johncotter.io. See the privacy policy and terms of use.