sudeux

The app icon: a 3×3 grid with the digits 1 to 9

Sudeux

A clean, native sudoku for the foldable iPhone Duo, for iPhone and for iPad.
No ads, no accounts, no tracking.

A puzzle on the iPhone Duo, with notes in four selected cells The puzzle list: four puzzles, one won without hints A puzzle in dark mode

Why it exists

Sudeux is built first for the iPhone Duo, the foldable iPhone, and for playing a puzzle next to something else: a video in picture in picture, or another app in split view. It has to work well at any window size, in every pose of the Duo (closed, open and half-open), in light and dark mode, with touch, Apple Pencil or a keyboard.

And it stays out of the way: no ads, paywalls, accounts or analytics. The only connection it makes is to your own iCloud, to sync your puzzles and finished lessons between your devices, and to continue a puzzle on another one with Handoff. Everything is native SwiftUI, following the platform’s own controls and conventions rather than a custom look.

Features

Puzzles that are fair

Four difficulties: Easy, Medium, Hard and Very hard.
Every puzzle has one solution and can be solved by logic alone; you never have to guess. Puzzles are generated on the device, and each one is graded by a solver that only uses techniques people use, from naked singles up to X-wings and beyond.
Several puzzles can be in progress at once.

Playing

Values and notes. Slide over the 3×3 number grid to enter several notes in one go. Entering a value clears that digit from the notes in its row, column and box.
Select several cells by dragging across the board, and add or clear a note in all of them at once.
Undo and redo hold a puzzle’s entire history, even after you leave it or restart the app.
Mistakes and hints. A wrong value is marked right away and locks the board until you undo it; three mistakes lose the puzzle (the limit can be changed). A hint fills in the correct value of a cell when you’re stuck, and a puzzle solved without hints earns a gem.
Haptics for notes, right and wrong values, and the end of a puzzle.

The win screen with confetti and a crown

Made for every screen

iPhone Duo in every pose, with its controls in the system’s side bar.
iPad in any orientation, in split view, with Stage Manager and while the window is resized.
Puzzles zoom open from their card and fold back into it.

A puzzle on the open iPhone Duo, with the number grid beside the board and the controls in the side bar

A puzzle on the half-open iPhone Duo: the board on one half of the screen, the number grid on the other

The same puzzle on the iPhone Duo open (top) and half-open (bottom), where the board and the controls each get one half.

A puzzle on iPad in landscape, with the number grid beside the board

Apple Pencil and keyboard

Apple Pencil Mode (on iPad, and on the iPhone Duo while it’s open flat) puts a small digit pad straight into the selected cell (and the cell the Pencil hovers over): tap a digit for a note, slide for several, touch and hold for the cell’s value. Double-tap and squeeze follow the system’s Apple Pencil settings, and there’s an eraser mode for notes.
Keyboard mode for a hardware keyboard: digits, arrow keys to move, Shift-arrows to select, and shortcuts for undo, redo and hints, all listed in the menu bar.

Apple Pencil Mode: a digit pad in the selected cell

Learn Sudoku

A course for each difficulty, from the rules and the game’s buttons in the Easy course to every technique the solver uses. Each lesson explains its technique, shows the step on a real board, and gives you boards to try it on yourself.
Hints that teach: after a hint, the app can say which technique proves the value, with a link to its lesson (it can be turned off in Settings).

Around the puzzle

A puzzle list with each puzzle’s difficulty, progress, hints and outcome (a crown for a win, a cross for a loss), swipe actions and a preview on touch and hold.
Widgets to continue your recent puzzle or start a new one, and one with your number of wins. Home Screen quick actions and Shortcuts do the same.
Eight colour palettes, plus Disco, which picks a new one after every win. The app icon follows the palette.
Accessibility: VoiceOver labels and announcements for every cell and change, Dynamic Type, Increase Contrast and Reduce Motion, and no information shown by colour alone.
English and Dutch.
Settings live in the Settings app, like the system’s own apps.
Diagnostics stay on the device. The app keeps a detailed log for finding bugs, which only leaves the device when you export it yourself.

A puzzle on iPad in dark mode

Running it locally

You need a Mac with Xcode 27.2 (the iOS 27.2 SDK). The app runs on iOS and iPadOS 27.0 and later.

Clone the repository and open sudeux.xcodeproj.
Choose the sudeux scheme and an iPhone or iPad simulator. For the foldable layouts, choose an iPhone Duo simulator; its pose can be changed in Device Hub.
Run (⌘R).

To run it on your own device, you need a paid Apple Developer Program membership: the app uses iCloud (CloudKit and the key-value store) and push notifications for sync, and Enhanced Security, which a free personal team can’t sign. Choose your team under Signing & Capabilities for the sudeux and SudeuxWidgetsExtension targets, and give the app identifiers of your own. They’re set once, as the project’s build settings APP_BUNDLE_IDENTIFIER, APP_GROUP_IDENTIFIER and ICLOUD_CONTAINER_IDENTIFIER, which the targets’ identifiers, entitlements and Info.plists read.

Tests and checks

All game logic lives in the local Swift package Packages/Logic, so most tests run without a simulator:

cd Packages/Logic && swift test -Xswiftc -O

(Optimised: the puzzle generator is about 100 times slower without it.)

scripts/check.sh hook runs what the pre-commit hook runs: the version check (CHANGELOG.md against the project), formatting (swift-format, part of Xcode), linting (swiftlint), a check that mutation testing can test every mutant from one build, the package tests, a build of the app and its tests, and the translation check (every text has its Dutch). scripts/check.sh full adds the snapshot tests, the UI tests and mutation testing, which needs swift-mutation-testing. To use the hook and install the tools:

git config core.hooksPath scripts/hooks

brew install swiftlint

brew tap ericodx/homebrew-tools && brew trust --formula ericodx/tools/swift-mutation-testing && brew install swift-mutation-testing

The UI tests (SudeuxUITests) run from Xcode or xcodebuild test on any simulator, with a store of their own, so they never touch your puzzles.

Project layout

Folder	What’s in it
`Sudeux/`	The app: SwiftUI views and system glue only
`SudeuxWidgets/`	The widgets
`Packages/Logic/`	`SudokuCore` (the game, generator and solver), `UILogic` (the screen’s decisions) and `AppServices` (storage, logs, settings, sync)
`SudeuxUITests/`	End-to-end tests
`SudeuxSnapshotTests/`	Snapshot tests: each screen compared with a reference picture per simulator
`scripts/`	The checks, and the scripts that draw the app icon, symbols and difficulty pictures
`docs/`	`PLAN.md`, the full design with every decision made while building it
`site/`	The app’s web pages: the privacy policy and the support page

AI disclosure

All code in this repository was generated by Claude Code.

Licence

Sudeux is licensed under the Apache License 2.0. The puzzle generator’s constraint propagation and uniqueness check are ported from sudoku.js (MIT); see NOTICE and THIRD_PARTY_NOTICES.md. The app icon, symbols and pictures are drawn from scratch by the scripts in scripts/.