LibreSudoku

LibreSudoku is, in its README’s words, an “Open Source sudoku application designed to be as user friendly and customizable as possible”. Its developer, Denis Repin (kaajjo on GitHub), started it in 2022; the release notes promise it “was and will be always free, without any subscriptions or ads”. It is a modern Material You app, with your phone’s colours by default.

Puzzles

• Classic and Killer Sudoku, each in 6×6, 9×9 and 12×12. Killer Sudoku, where cages of cells must add up to a given sum, came in version 2.0.
• Four difficulties: Easy, Moderate, Hard and Challenge. The developer explains that the app “grades the difficulty of a sudoku based on the techniques required to solve it.”
• Generated on the phone, so there is no fixed set to run out of. The generator is a modified version of QQWing, and the app keeps a new puzzle only if it has exactly one solution.
• Your own puzzles: type one in or paste it as a string of digits (36, 81 or 144 characters, with 0 or . for empty cells); the app saves it only if it has a single solution. You can also import 9×9 collections in the .sdm, OpenSudoku and Sudoku 10’000 formats and keep them in folders. One user reported in 2026 that OpenSudoku files crash the import or fail; there is no reply from the developer yet.
• Export: a folder as an .sdm file, or the current board as a one-line string, which the developer suggests checking on solver websites.

Playing

• By default you pick a number first and then tap the cells for it (“Value first”); “Cell first” works the other way round.
• Notes with automatic erasing, a Compute notes option that fills in all candidates, and undo and redo (long-press undo).
• Mistake checking in three modes: off, rule violations (the default) or comparison with the solution. A limit of three mistakes per game is optional and off by default.
• Hints: a hint fills in the selected cell from the solution and adds 30 seconds to your time. An experimental Advanced hint, off by default, instead explains a step: a wrong value, a full house, a naked single or a hidden single. You can also turn hints off entirely.
• Learn: short lessons on the rules, the basic method, naked pairs and hidden pairs.
• Statistics for each difficulty and type: best and average times, win rate, streaks and your five best games. The app warns that “a win streak will be reset if you lose (reach the mistakes limit), give up, or start a new game without finishing the previous one”.
• Backups: your games, folders and records, plus settings if you like, saved to a file, and automatic backups to a folder you choose, from daily to weekly, keeping up to five copies.
• Settings include highlighting the row and column and identical numbers, a count of each number’s remaining uses on the keypad, and keeping the screen on (on by default). The app is translated into about 30 languages, Brazilian Portuguese among them.

What it connects to

Nothing on its own. This is the FOSS edition, which has no internet permission. Since version 2.0.2 the developer publishes two: FOSS, and “nonFOSS”, which adds an in-app updater and the internet and install permissions it needs. In this one, the updater code is switched off and its settings are hidden, although the networking library and the update address are still in the code, unused. The links in the About screen (GitHub, the Weblate translation site and a Telegram channel) open in your browser only when you tap them. If the app crashes, it shows the log and offers to copy it and open a new GitHub issue; nothing is sent automatically. The About screen also lists cryptocurrency and card donation details, which are copied when tapped.

The permissions it lists

The APK lists four permissions: running a foreground service, starting at boot and keeping the phone awake, plus an internal one that only apps with the same signature can use. All of them come from Android libraries, not from LibreSudoku itself (see the questions below).

About this file

• This is the developer’s own FOSS build of version 2.0.2, signed by Denis Repin, from IzzyOnDroid. It is the same file, byte for byte, as the FOSS APK on the project’s GitHub releases and F-Droid’s download, which F-Droid builds from source and checks against the developer’s release. Updates from any of the three install over each other. The app’s About screen calls it 2.0.2-FOSS.
• Version 2.0.2, from March 2025, is still the latest release; its release notes mention only the split into the two editions. The code has kept changing since: in October 2026 a new puzzle generator and difficulty rating were merged, not released yet.
• The 4.1 MB file runs on ARM and x86 and needs Android 8.0 or later. Our scan found no trackers.
• The screenshots are the project’s own, from three days after the 2.0.2 release; we left out one that shows the nonFOSS edition’s update setting, which this edition doesn’t have.
• LibreSudoku is licensed under the GPL-3.0; its QQWing-based generator is GPL-3.0 or later.

CPU types in this build: arm64-v8a (64-bit ARM, almost every phone since 2017); armeabi-v7a (32-bit ARM, older and budget phones); x86 (32-bit Intel, emulators); x86_64 (64-bit Intel, emulators and Chromebooks).

Versions currently kept in the IzzyOnDroid repository. We host and check only the newest one. Full changelog.