Click cells on the grid
Click a cell, then type a digit to correct OCR errors. Backspace clears a cell. Duplicate digits are highlighted in red.
The candidates view shows, for each unsolved cell, which digits are still possible — and highlights which digits appear in every valid solution for that cage.
Press Show candidates to reveal the candidate grid. Each unsolved cell displays up to nine small digits arranged in a 3×3 layout matching their position on a keypad:
1 2 3 4 5 6 7 8 9
A digit that does not appear has been ruled out. A digit shown in grey is possible but not yet certain. A digit shown in salmon is essential to that cage.
A digit is essential for a cell if it appears in every remaining valid solution for that cell’s cage. Essential digits are worth paying close attention to when you are stuck.
The Auto / Manual toggle controls how the candidate grid is maintained.
Auto mode (default): the app computes candidates for you. When you place a digit in any cell, candidates in related cells are immediately updated.
Manual mode: you manage candidates yourself. The app does not eliminate or promote anything.
Switching from manual to auto merges your work with the solver’s knowledge: for each digit in each cell, the more restrictive of the two assessments wins.
Switching from auto to manual leaves your candidate marks exactly as they are.
Press Edit candidates to enter candidate editing mode. Each digit cycles through its states:
Press Delete (or Backspace) in candidate editing mode to reset the selected cell to its auto-computed state.
When you enter a digit into a cell, its candidates are hidden but not lost. If you undo or clear the digit, the candidates reappear exactly as you left them.
COACH reads a photo of a killer sudoku puzzle, detects the cage layout and totals, and guides you through solving it using logical deduction rules. It never guesses — every suggestion is a logically valid elimination or placement.
Press Show candidates to see which digits remain possible in each unsolved cell. A salmon digit is essential — it appears in every valid cage solution. Press ? for full candidates help.
Press Hints to see available logical deductions. Each hint explains the rule it used and what it eliminates. You can apply it automatically or work through it by hand.
Open Config to choose which rules run automatically after every move. Rules left as hint-only appear in the Hints list. Press the ⓘ button next to any rule for an explanation.
When you can deduce that a set of cells sums to a known value, press Virtual cage, click the cells, and enter the total. The app will track valid solutions for this cage and use it in future hints.
The digit images extracted from your puzzle will be sent anonymously — 64×64 pixel thumbnails of cage total numbers only. No puzzle layout, personal information, or newspaper image is included.