Star Grid

About this game

Star Grid is the logic puzzle usually called Star Battle. A square grid is cut into irregular coloured regions, and your job is to place stars so that every row holds exactly one, every column holds exactly one, and every colour holds exactly one — with the extra condition that no two stars may sit next to each other, not even diagonally at a corner. That last rule is the one doing most of the work. It sounds like an afterthought and it is actually the engine of the puzzle: a star does not merely claim its own row and column, it poisons the eight squares around it, and chasing that fallout through the colours is where the deductions come from. What separates this from most versions is what happens before a grid reaches you. Each one is dealt, then checked twice: once to prove that exactly one arrangement of stars satisfies it, and again to prove that a solver restricted to human techniques can actually reach that arrangement. Grids that fail either test are thrown away and never shipped, so the promise is a strict one — you will never need to guess, and you will never arrive at the end to find two possibilities left standing. The difficulty labels mean something specific, too. They are not grid size dressed up. Every grid is rated by the hardest technique it genuinely forces, which is tested by switching that technique off and asking whether the grid still falls: Easy grids need only spot the last square left in a row, column or colour; Medium grids force you to notice that a colour is confined to a single line; Hard grids force the same argument across several colours at once; and Expert grids cannot be finished without assuming a star, following it until something breaks, and ruling it out. Grids run from seven squares across up to ten. A hint reads the board as you have actually left it, names the next square that is forced and explains why it is forced — and if you have placed a star that cannot be right, it tells you that instead. A new grid arrives every day, gentle at the start of the week and expert on Sunday, with a streak to keep, hint-free solves counted separately, and a link you can send to deal a friend the exact grid you just played.

Controls

Tap a square once to pencil it out, again to place a star, and once more to clear it. Dragging across empty squares pencils out a whole run of them at once.

Keyboard

• Arrow keys move the cursor around the grid.
• Space or Enter cycles the square under the cursor.
• X pencils a square out, and back in again.
• Z undoes, H asks for a hint, R resets the grid.

How to play

Every row, every column and every colour must end up holding exactly one star.

The rules

• No two stars may touch, not even diagonally at a corner — this is the condition that makes the puzzle a puzzle rather than a counting exercise.
• The colours are irregular. Some sprawl across half the grid, some are a single square, and a single-square colour is a star handed to you for free.
• Every grid has exactly one answer, and it can always be reasoned out. If you are stuck, something on the board is deducible.

On the board

• Tap once to pencil a square out, twice to place a star, three times to clear it.
• Pencil marks are yours to use as you like — they are never checked and never wrong, so mark freely.
• Stars that break a rule turn red and the Clashes counter rises, so a mistake shows immediately rather than at the end.
• Undo and reset are free, and a hint will name the next forced square and the reason it is forced.

Read the full Star Grid rules and strategy →