Why Suuudokuuu Is an Ad-Free, Open-Source Sudoku

Updated 11 August 2026

Suuudokuuu is a free sudoku app and website with no ads and no account, and the game itself carries no tracking of any kind. The full source — the puzzle generator, the solvers, the technique detector and the app itself — is published on GitHub under the MIT license. That combination is unusual: most sudoku apps run ads, most closed source apps ask you to trust their claims about privacy, and few publish the code that generates and checks the puzzles you are actually solving. This page lays out exactly what Suuudokuuu does, with links to the parts of the codebase that back each claim, so none of it has to be taken on faith.

What free and open source actually means here

Free means every difficulty level, every hint and every technique guide is available with no paywall, no subscription and no in-app purchase. Open source means the repository is public, the license is MIT — one of the most permissive licenses that exists, letting anyone read, fork, modify or redeploy the code — and every commit that ever shipped a feature is visible in the same public history. Nothing about generation, solving or scoring happens on a server you cannot inspect; the logic lives in plain TypeScript packages anyone can read end to end.

No ads, no account, no tracking in the game

The game ships with no advertising SDK, no analytics SDK and no crash-reporting SDK — nothing in the app’s dependency list sends your play activity anywhere. This website uses cookieless, anonymous page analytics to see which guides help people, with no cookies, no cross-site profiles and no ad networks; the game never does. Playing does not require creating an account, entering an email address or signing in with a third party. Progress, streaks and settings are stored on your own device, not in an account database, because there is no account database. If you want to verify this instead of trusting a marketing sentence, the dependency manifests are public, and you can grep them for yourself.

How this differs from most sudoku apps

The typical free sudoku app is free to download and monetized afterward: banner ads between puzzles, interstitial ads on mistakes, rewarded-video ads for hints, or analytics SDKs that report how you play back to an ad network. None of that is inherently dishonest — it pays for development — but it means the app’s incentives are not purely about helping you solve puzzles well. Suuudokuuu has no advertising business model to serve, so there is no interstitial timed around a wrong guess and no hint gated behind a video. The app either helps you learn to solve sudoku, or it does not; there is no third incentive pulling in a different direction.

Puzzles that are actually verified, not just generated

Every puzzle Suuudokuuu generates is checked for exactly one solution before it is served, using a solver-backed uniqueness check in the generator itself — no puzzle ever requires a guess to finish. The hardest tier goes further: Hell-difficulty puzzles come from a bundled, pre-verified 17-clue corpus, and 17 is the proven minimum number of clues a sudoku can have and still keep a unique solution. Those puzzles are additionally cross-checked by two independent solving algorithms — a Dancing Links exact-cover solver and a typed-array bitmask solver — so one algorithm’s bug cannot silently ship a broken puzzle. All three solvers, solver-dlx, solver-bitmask and the shared solver-core contract they both implement, are separate open packages in the repository, not a black box.

Hints that teach, not just answer

Stuck on a cell, most apps just fill it in. Suuudokuuu’s hint button runs the same technique detector that powers the technique guides on this site, so it names the exact pattern that justifies the next move — a hidden pair, a pointing triple, an X-Wing — and walks through why it applies, instead of silently revealing a digit. If you would rather work through a puzzle you already have on paper or from another source, the step-by-step solver does the same thing: type in a grid and it narrates every move by name, in your browser, with nothing sent to a server.

A transparent alternative

If you are comparing sudoku.com, other ad-supported sudoku sites, or a closed-source mobile app against Suuudokuuu, the practical difference is verifiability. You do not have to trust a privacy policy’s wording, because there is no hidden layer for it to describe — the code that generates your puzzle, checks it has one solution and decides what a hint tells you is public, readable and forkable on GitHub. That is the whole pitch: not a longer feature list, just fewer things you have to take on trust. It is also built to be comfortable, not just honest — see the sudoku for seniors guide for the large-print and comfort-mode options that come with the same free, ad-free package.