About Lacuno

Lacuno is a daily logic puzzle. Three symbols, three attempts, one right answer.

For how to play, see the rules page. This page is about what Lacuno is, why it works, and an honest look at whether puzzles like this actually make you smarter.

How is it different from Sudoku?

Sudoku is about variety: each digit must appear exactly once per line. You reason about what's missing.

Lacuno is about result: each line must combine to a specific target. You reason about what balances. A row of five ■s is fine, if the target is ■.

The depth underneath

What looks like a small three-symbol grid is actually an exercise in one of the foundational structures of mathematics — the cyclic group of order three. You don't need to know that. But you might enjoy noticing patterns in how the symbols behave, and finding shortcuts that make solving faster. That is, in a quiet way, real algebra.

Does it make you smarter?

Probably not in the way brain-training apps claim. The research on puzzles improving general intelligence is weaker than the marketing suggests — you mostly get better at the thing you practise, not everything else. Some of the best-known brain-training apps have been fined for overstating what they do.

What I can honestly say is that Lacuno uses the same moves as algebra — substitution, consistency-checking, inference from what you already know. Whether that transfers to anything else is a real open question.

What I know for sure is that when it clicks, it feels good. That's reason enough to play.

Questions people ask

Is Lacuno free to play?

Yes. The web version is free and always will be. No ads, no subscriptions, no account needed.

Do I need an account?

No. Open the page and play. Your progress is saved in your browser, on your device.

How long does a puzzle take?

It depends on you. The daily is designed to be a short break, not a long session.

Is there a new puzzle every day?

Yes. A new puzzle appears at midnight in your local time zone. Every player worldwide solves the same one each day.

Is Lacuno like Sudoku?

They're cousins, not twins. Sudoku asks you to avoid repetition — every digit once per line. Lacuno asks you to hit a target — the symbols in each line must combine to a specific result.

Can I play Lacuno on my phone?

Yes. The web version works on any phone browser. A native iPhone app with unlimited play is coming — sign up on the app page.