Press
Everything an article about Sudoku Still needs: a short description, full-resolution images, the icon, the measurements behind the difficulty scale, and the list of techniques the solver knows. All free to use.
In one sentence
Sudoku Still is a sudoku for iPhone and iPad that teaches you sudoku: 20 lessons and hints that name the technique before they name the digit. No ads, no tracking, no account.
In one paragraph
Most sudoku apps only check that a puzzle has exactly one solution. Whether a person can find it without trial and error is a different question. Sudoku Still also runs every board through a solver that knows only human techniques, and discards what it cannot finish. Both things follow from that: the promise that guessing is never required, and a difficulty level that depends on the hardest technique a puzzle needs rather than on how many digits are missing. And because a puzzle checked that way can be explained end to end, hints can work in steps: first where to look, then which technique applies, and only last the digit. 20 lessons show the techniques on real boards, and the statistics record, per technique, whether you spotted it yourself or had it shown to you.
At a glance
| Name | Sudoku Still |
|---|---|
| Developer | independently developed in Germany |
| Platform | iPhone and iPad, iOS 26 or later |
| Price | free, with an optional subscription “Sudoku Still Plus” for “Hard” and “Expert” in free play. The Daily Challenge is free on every level. |
| Languages | English and German |
| Data | nothing collected, no tracking, no account, no ads, no analytics SDK. Progress lives in the user's own iCloud key-value store. |
| App Store | apps.apple.com/app/sudoku-still |
| Contact | support [at] kornelius.org |
The numbers behind it
Measured on the generator's raw output: 10,000 dug candidates, with no target band and no filtering, graded with the same technique cascade that runs in the app.
- The clue count says almost nothing Between the number of givens and the hardest required technique there is a Spearman rank correlation of rho = 0.022 (n = 7,395, p = 0.056). “Fewer digits means harder” is not true.
- 26.1 percent discarded On 2,605 of 10,000 candidates the cascade fails: they would only be solvable by guessing or backtracking. Those are exactly the ones the app never ships.
- Two techniques never came up In 10,000 candidates, Jellyfish and Hidden Quad were never once the hardest required technique. The solver knows them anyway, the app just never demands them.
The full measurement, with tables and method, is in the app's source repository
(docs/vorgaben-und-schwierigkeit.md); the measuring program compiles the app's
own engine, so the numbers do not come from a second implementation.
Techniques the solver knows
Every one of them is explained in the tutorial, and none is ever required without being taught there.
- Naked Single
- Hidden Single
- Pointing Pair
- Claiming
- Naked Pair
- Hidden Pair
- Naked Triple
- Hidden Triple
- Naked Quad
- Hidden Quad
- X-Wing
- Swordfish
- Jellyfish
- XY-Wing
- XYZ-Wing
- W-Wing
- Unique Rectangle
- BUG+1
Images
Click an image for the full resolution. iPhone 6.9 inch, captured from the running app.
No ads. No tracking. No account.
Full size, 1320 px
Hints name the technique, not just the digit.
Full size, 1320 px
20 lessons with guidance.
Full size, 1320 px
Every technique shown on a real board.
Full size, 1320 px
One puzzle a day, the same for everyone.
Full size, 1320 px
Your progress for every technique.
Full size, 1320 px
Notes tidy themselves up.
Full size, 1320 px
Every solved game is in your history.
Full size, 1320 px
App icon
sudoku-still-icon-1024.png, 1024 by 1024 pixels, no transparency.
Use
Images, icon and text on this page may be used freely for coverage of Sudoku Still. Questions, further images or an interview: support [at] kornelius.org. We reply personally.