How to play SunMoon
SunMoon is a binary logic puzzle solved by pure deduction. Here are the rules and the techniques that crack every board.
The rules
- Every cell holds one of two symbols: a ☀️ sun or a 🌙 moon.
- No three identical symbols may sit next to each other in a row or column.
- Each row and each column contains an equal number of ☀️ and 🌙.
- A = clue between two cells means they are the same; an ✕ clue means they differ.
- Some cells are given at the start (locked).
Controls
- Tap an empty cell → ☀️. Tap again → 🌙. Tap a third time → clear.
- Given (locked) cells can't be changed.
- Cells that break a rule are outlined in red.
Solving strategies
- Avoid triples. If two identical symbols sit side by side, the cells on both ends must be the opposite symbol.
- Fill the gaps. A single empty cell between two identical symbols must be the opposite (otherwise you'd make three in a row).
- Count to the balance. Once a row or column has all of one symbol placed (N/2), every remaining cell in that line must be the other symbol.
- Use the clues. An ✕ forces opposites, an = forces a matching pair — chain these with the no-triple rule for quick wins.
A worked example
Say a row on a 6-wide board starts ☀️ ☀️ and the rest is blank (three suns, three moons per row). The two suns force the third cell to be 🌙 — three suns in a row is illegal. That moon plus the balance rule then constrains the rest: you still need one sun and two moons across the last three cells, and the no-three rule blocks any run from forming. Chaining "no triples" with "balance" like this resolves most of a board before you even use the = / ✕ clues.
Common mistakes
- Ignoring balance until the end. The equal-count rule applies from move one — as soon as a line has all its suns (or moons) placed, every remaining cell is forced.
- Misreading clues. = means the two cells match; ✕ means they differ. Swapping them cascades into contradictions.
- Filling fast and making a triple. Three identical symbols in a line is always illegal — check both directions before you commit a cell.
Frequently asked questions
- What kind of puzzle is SunMoon?
- It's a Tango-style binary logic puzzle — the "two-symbol" grid family, with no-three-in-a-row, balanced lines, and equals/opposite clues.
- Do I ever need to guess?
- No — every board is generated to be solvable by logic alone, and rule-breaking cells are outlined in red so you can backtrack.
- Is there a daily puzzle?
- Yes, plus unlimited random boards — free and with no login.