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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 put you on the right track instead of giving away 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 which technique applies and in which area, then the exact spot, and only last the digit. 17 of the 20 lessons show their technique 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 |
|---|---|
| What it is | Sudoku for iPhone and iPad, with lessons and hints |
| Developer | Kornelius, independent |
| Based in | Germany |
| Devices | iPhone, iPad and iPhone Duo |
| Requires | iOS 26 or later |
| Languages | English, German |
| Price | Free, with an optional subscription “Sudoku Still Plus” for “Hard” and “Expert” in free play. The Daily Challenge is free on every level. |
| Released | 29 August 2026 |
| App Store | apps.apple.com/app/sudoku-still/id6792647620 |
| Website | kornelius.org/sudoku |
| Data collection | None. No tracking, no account, no ads, no analytics SDK. Progress lives in the user's own iCloud key-value store. |
| Contact | support [at] kornelius.org, personal reply |
Table as of 7 October 2026. Release date, devices, requirement and languages are taken from the App Store listing.
The numbers behind it
Measured on 30 August 2026 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
App preview
The same recording as the App Preview on the App Store, without sound.
The title cards in the video, in order:
- No ads. No tracking. No account.
- Stuck? The hint names the technique.
- Every technique has a lesson.
- Solved without guessing.
On iPhone Duo
From version 1.5 Sudoku Still uses every pose of iPhone Duo. Open and sideways, the board takes one half of the inner display and the digits the other, with the tools in the bar at the edge. Half open on a table, the board stands on top and the controls lie below. Closed, the header and the tools move into the bar, and the board gains their height.
Images
Click an image for the full resolution. iPhone 6.9 inch, captured from the running app.
Download all 8 images and the icon as a ZIP, 1.7 MB
No ads. No tracking. No account.
Full size, 1320 px
Hints put you on the right track.
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20 lessons with guidance.
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Techniques shown on a real board.
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One puzzle a day, the same for everyone.
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Your progress for every technique.
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Notes tidy themselves up.
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Every solved game is in your history.
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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.