Sudoku for iPhone
Sudoku that never needs a guess
Every grid is checked to have exactly one solution, and its difficulty is the hardest technique the solver actually had to use to get there — not a count of blank squares. Take a breath and fill the grid.
Download on the App Store
iPhone · free · no ads, no account, works in airplane mode
537619598686348317266284195879
- 5difficulty levels
- 11techniques graded
- 1solution, always
- 0ads and accounts
What you actually get
Difficulty that means something
Most sudoku apps decide difficulty by how many squares they erased. That is a terrible proxy: a grid with 24 givens can fall to nothing but singles, and one with 32 can need an X-Wing. Here the generator solves each finished puzzle with human techniques only, records the hardest one it needed, and that technique is the difficulty. Beginner means naked singles. Easy adds hidden singles. Medium reaches pointing pairs, claiming and naked pairs. Hard reaches hidden pairs and naked triples. Expert is X-Wing, Swordfish and XY-Wing territory.
Exactly one solution, verified
Every puzzle is dug out of a completed grid one symmetric pair of cells at a time, and after each dig the solver counts solutions with an early exit at two. If the count is not one, the dig is undone and the generator moves on. So a puzzle can always be finished by reasoning alone, and no branch you follow correctly can ever turn out to be the wrong branch.
Hints that teach instead of telling
Three hints per game. A hint does not just drop a digit in — it runs the same cheapest-first cascade a person would, names the technique it landed on, and highlights the cells that make the deduction work. If you would rather not read the reason, the digit is right there too. If the board already contains a mistake, the hint says so instead of pretending the position is sound.
Pencil marks that keep themselves tidy
Notes are a nine-bit mask per cell, so a cell holds any combination of candidates with no bookkeeping. Turn on auto-fill and the board pencils in every legal candidate for you. Enter a digit and that digit is stripped from the notes of every cell that shares its row, column or box — the part of paper sudoku that is pure clerical work, and the part where paper players lose games.
A daily challenge everyone plays
The daily puzzle is derived from the calendar date by a hash, not fetched from a server. It is a pure function, which means your phone and a stranger’s phone in another timezone generate the same grid without either of them going online. The home screen keeps a month calendar of the days you finished.
Statistics worth looking at
Games played and solved, completion rate, current and best day streak, total time, and then per difficulty: played, won, best time, average time, and flawless wins — the ones you finished without a single wrong digit. All of it is computed from the game records themselves, so nothing can drift out of sync with reality.
Five themes, one of them dark
Pure White, Forest Green, Sky Blue, Cherry Blossom and Deep Space. Each one sets the page, the board, the box rules, the selected cell, the peer highlight, the same-digit highlight and the conflict colour as a set, so the grid stays readable rather than merely tinted.
Nothing in the way
Optional mistake highlighting, optional same-number highlighting, optional haptics, undo, a pause that blanks the board, and a timer you can ignore. Nine interface languages, or follow the system. No banner, no interstitial, no daily-reward popup, no login wall.
How a puzzle gets its difficulty
Difficulty is measured, not assigned. This is the whole procedure, and it runs on your phone in a few milliseconds.
- Fill a complete gridA seeded random walk with constraint propagation produces a finished, valid 9×9 solution. The seed comes from a small deterministic generator, never from the system clock mid-run, so the same seed always yields the same grid.
- Dig holes in symmetric pairsCells are removed two at a time in 180°-rotational pairs, so the finished puzzle looks like a puzzle rather than a random spatter. A second, asymmetric pass follows if the target still has not been reached.
- After every dig, count the solutionsThe solver counts solutions with an early exit at two. Anything other than exactly one and the pair goes straight back in. This is the step that makes guessing unnecessary.
- Solve it again with human techniques onlyA cascade runs cheapest technique first: naked single, hidden single, pointing pair, claiming, naked pair, hidden pair, naked triple, X-Wing, Swordfish, XY-Wing. The hardest one it needed is the grade.
- Accept or throw it awayIf the grade does not match the level you asked for, the puzzle is discarded and the generator tries the next seed. Expert is the one band allowed to require trial and error, and even there the solution is still unique.
The floor on givens is 40 for Beginner down to 22 for Expert, with a hard floor of 17 — the proven minimum for a sudoku with a unique solution.
What leaves your phone
Nothing. This is not a positioning statement, it is a property of the build: the app contains no HTTP client, no analytics SDK, no advertising SDK and no backend.
Puzzles are generated on the device. The daily challenge is derived from the date rather than downloaded. Your games, your statistics and your settings live in a local database and a local keychain entry, and are deleted with the app.
There is no sign-up, no email, no device identifier collected and no tracking. The App Store privacy label reads Data Not Collected, and the bundled privacy manifest declares an empty set of collected data types.
The only links that leave the app are the privacy policy, the terms and the support address in Settings, and those open in Safari or Mail — the app itself never makes a request.
Price
Free. Every difficulty, the daily challenge, hints, notes, statistics and all five themes are in the app from the first launch.
There is no subscription, no consumable, no rewarded video and no energy meter. Nothing in the game is gated behind watching or paying for anything.
Download on the App Store
Questions people ask first
Can a puzzle ever be impossible?
No. Every puzzle is verified to have exactly one solution before it is handed to you, and for every level except Expert it is also verified to be reachable by human techniques within that level’s band. If you are stuck, a deduction exists — the hint will name it.
Do I need an internet connection?
Never, including for the daily challenge. The generator and the solver both run on the phone.
Is the daily puzzle the same for everyone?
Yes. It is a pure function of the local calendar date, so any two devices set to the same date produce the same grid. Nothing is fetched, so nothing can be different.
Does making a mistake end the game?
No. Mistakes are counted, and highlighted if you leave that setting on, but there is no three-strikes rule and no forced restart. A game finished with zero mistakes is recorded as a flawless win in your statistics.
What happens to my games if I delete the app?
They are gone. Everything is stored locally and nothing is backed up to a server, because there is no server.