Logic puzzle

Ondulo

Probe the field, find the hidden modules

Ondulo is a free online logic puzzle where you locate 4 modules hidden in an 8×8 field by sending waves in from its edges and reading where they come out, with a new puzzle every day.

Duration: 5–8 min
Difficulty: Hard
Skill: Deduction
Price: Free

Play now — for free

How to play?

Four modules hide in an 8×8 field: you know their shape and colour, not where they sit. Send waves in from the edges: each one comes out somewhere, tinted by the coloured modules it touched. Cross the signals, drag the modules onto the field, then submit: your probes replay on your layout. All with as few probes as you can.

Tap an arrow on the edge, then tap it again to send a wave.
The wave comes out through another port, bounced by the modules it meets.
Its colour mixes those of the modules it touched: red and blue make purple.
Drag the four modules onto the field, tap one to rotate it, then submit: the waves replay on your layout.

Why play?

A true deduction game, where every probe counts.
The same field for everyone, every day.
Time is not part of the score: only the sharpness of your reasoning counts.

Tips

An echo, a wave leaving through its own entry port, always means a flat face somewhere on its path: a bar or a triangle's straight side. A diamond always turns waves at a right angle.
A white wave touched no coloured module, but it may have bounced off a white one. If it does not exit straight across from where it entered, a white module deflected it.
Read colours as a mix: purple means red and blue were touched, black means all three primaries. Each module tints the wave only once, even if the wave hits it several times.
Place your guesses as you probe: they are free and stay on your device. Only submit once every signal in your history is explained: a wrong answer weighs as much as 2 probes. When you submit, every wave replays on your modules and a red cross marks those that disagree.
Time is not part of the score. Take your time to reason before each probe: beyond the first 4, every extra probe lowers your score.

Frequently asked questions

How do you play Ondulo?

Four modules, whose shape and colour you know, are hidden in an 8×8 field. Tap an arrow on the edge twice to send a wave: it exits through another port, bounced and tinted by the modules it touched. Drag the modules onto the field, tap them to rotate, then submit: your probes replay on your layout.

Is Ondulo free to play?

Yes. Ondulo is free in your browser, on desktop or mobile, with nothing to download. You can play today's field without an account. A free account unlocks the archive of past days, and SIWA+ (18 € a year) removes ads and adds advanced stats.

Do I need to find the exact position of every module?

Not necessarily. Your answer is accepted if it uses the four announced modules, with no overlap, and if all 32 ports return exactly the same exits and colours as the real layout. Two layouts that no probe can tell apart are both correct.

What do the wave colours mean in Ondulo?

Each coloured module a wave touches adds its colour: red, blue or yellow. Mixes give purple (red and blue), orange (red and yellow), green (blue and yellow) and black (all three). A white wave touched only white modules, or none at all.

How is the Ondulo score calculated?

The score is out of 1000. The first 4 probes are free, then each extra probe takes off 50 points. A wrong submission counts as an error, which weighs as much as 2 probes (−100). Time is not counted and there is no joker: only the quality of your reasoning matters.