doku.su: Sudoku Coach

Sudoku. Now it clicks.

With doku.su, every puzzle is a chance to learn. Your coach helps you spot the next move and understand why it works.

A LITTLE HINT. A BIG AHA.
Ask for a clue from your current grid. Reveal the reasoning one step at a time, then make the move yourself. You choose how much help to see.

LEARN ONE METHOD AT A TIME
Start with rows, columns and 3 × 3 boxes. Follow a worked example, try the idea yourself, then explore candidates, pairs and more advanced techniques.

YOUR PUZZLE. YOUR COACH.
Import a photo or enter a grid. Photo recognition happens on your device, and you check the numbers before playing.

MAKE YOUR NEXT LITTLE BREAKTHROUGH
Come back to a daily puzzle, your lessons and your progress. Local puzzles remain available offline. An optional account lets you sync your progress.

Free includes a daily puzzle, unlimited undo, beginner lessons, full coaching until your first coached success, one support thread on each later puzzle, and basic progress tracking.

The optional monthly Coaching subscription unlocks unlimited puzzles and support, advanced and full-grid Guided solve, every proof replay, the full lesson library, personalized practice, spaced mistake review, and complete progress history.

The regional price is shown before purchase. Payment is charged to your Google Play account. The subscription renews automatically unless cancelled in Google Play settings before the renewal date. Cancelling stops renewal while keeping access through the verified paid end date. Verified grace keeps access through its end; payment hold, expiry, or revocation ends access. A refund record alone changes access only if Google also ends or revokes the subscription. Restore with the same Sudoku Coach account and wait for server verification, or open Google Play subscription settings from Account. Deleting the Sudoku Coach account does not cancel Google Play billing.

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Support: https://doku.su/support