About Solsticio
Solsticio is a free daily sun and moon logic puzzle — a binary puzzle in the Takuzu / Binairo family — playable in the browser and as a mobile app. It is made by Carlos Marcos, an independent developer, and it gives everyone the same new board every day — one you can always solve by logic, without guessing.
Who makes it
Solsticio is made by Carlos Marcos, an independent developer who designs and builds the puzzle generator, this website and the app. Questions, bug reports and ideas for the game are welcome at [email protected].
How the daily puzzle is made
A daily puzzle only works if it is fair and the same for everyone. In Solsticio both things are properties the code checks, not promises:
- The date is the seedEach day's puzzle is computed from the date alone by a deterministic generator. No server decides it, so the website and the app show exactly the same board to everyone, everywhere — and the app can work fully offline.
- A 6×6 boardThe daily is a 6×6 grid: three suns and three moons in every row and column, and never three alike in a line.
- Exactly one solutionBefore a board is accepted, the solver must finish it by pure deduction, without a single guess. That guarantees one solution — and that you never need to guess either.
- Difficulty is measuredA board is rated by the deduction techniques the solver actually needed, from spotting a blocked trio up to reasoning by contradiction — not simply by counting the given cells. The daily is chosen from a fixed difficulty band.
The daily videos on Solsticio's social accounts are generated from the date too, but on purpose they use a different board, so they never spoil today's puzzle.
The engineering, with code, is on the blog: A daily logic puzzle with no backend at all and Rating logic puzzles by the deductions they require. The same techniques, explained for players, are on the how to solve page.
Where to play
Today's puzzle is free in your browser, with nothing to install and no sign-up. On your phone, the free Android app adds hundreds of levels, the Daily Puzzle with streaks and a monthly calendar, a Zen mode for unhurried solving, and pencil marks to try an idea without it counting as a mistake. It works 100% offline, needs no account, uses colour-blind friendly symbols that differ by shape, and is available in English, Spanish, Portuguese, French and German.
Official profiles
Solsticio's official accounts, where the daily puzzle is posted:
- Bluesky — bsky.app/profile/solsticio.app
- Mastodon — mastodon.social/@solsticioapp
- YouTube — youtube.com/@solsticioapp
- Instagram — instagram.com/solsticioapp
- Threads — threads.com/@solsticioapp
- Pinterest — pinterest.com/solsticioapp
- Telegram — t.me/solsticio_daily
- DEV — dev.to/solsticioapp
- Hashnode — solsticio.hashnode.dev