Good puzzles. Generous people.

Credit where it's due.

GridZero's 8,000 bundled puzzles come from Grant McLean's Sudoku Exchange puzzle bank, created for Sudoku Exchange. Thank you for making this collection freely available.

The upstream puzzles were generated with Stephen Ostermiller's QQWing and rated with SudokuMonster's Sukaku Explainer. Those tools are credited for the dataset; GridZero does not embed their engines. Our on-device generator is our own implementation.

Free really means free

The dataset is dedicated to the public domain under the Unlicense. GridZero's app code and original artwork are MIT licensed.

The same collection everywhere

iOS, Android, and the browser all use one checked resource: 2,000 Easy, 2,000 Medium, 2,000 Hard, and 2,000 Expert puzzles. Expert maps to upstream Diabolical. Original puzzle IDs and ratings are preserved, and each bundled board is independently checked for exactly one solution.

The pinned upstream revision is d8c8ebaee0c0. The larger upstream bank contains 893,916 records at that revision; this release bundles a reproducible selection, not the entire bank.

Read our data provenance notes for the selection process and future expansion plan.