What is Star Battle?
Star Battle is a logic puzzle on a square grid divided into color regions: place stars so that every row, every column and every region contains exactly the same number of stars, and no two stars touch, not even at a corner. Newspapers print the 10×10 two star version under the name Two Not Touch.
Three rules, but they interlock. The moment a star lands, its eight neighbors are ruled out, the free spots in its row, column and region shrink, and that change ripples into the next region. In this version a placed star sparkles in gold, touching stars and overfilled lines turn red, and when the last star drops the stars link up into a constellation and lift into the sky.
How many stars per board size?
5×5 and 6×6 take one star per row, column and region; 8×8 and 10×10 take two stars. Two star boards are much harder because the no touching rule bites far more often.
| Board | Stars per row, column, region | Total stars | Difficulty |
|---|---|---|---|
| 5×5 | 1 | 5 | Starter. Learn the rules |
| 6×6 | 1 | 6 | Easy. Two or three minutes |
| 8×8 | 2 | 16 | Medium. The daily puzzle size |
| 10×10 | 2 | 20 | Hard. The standard competition size |
Every board is generated on the spot. The game first scatters a valid set of star positions, grows the color regions out from those stars as seeds, then runs a solver to confirm the answer is unique. If more than one answer exists it moves cells of the rival answer into neighboring regions and checks again, and if that fails it starts over. The result is a board that can always be finished by pure deduction, never by guessing.
Where do I start deducing?
Look first at the smallest regions and any region that fits inside a single row or column. A region must hold its own stars, so the rows and columns it occupies cannot lend those stars to anyone else.
| Technique | Why it works |
|---|---|
| Region inside one row | That region's star is that row's star, so every other cell in the row is a dot |
| Two regions inside two rows | The two regions use up both rows' stars, so the rest of those rows are dots |
| One star per 2×2 | Stars cannot touch, so any 2×2 square holds at most one star. A region that must put a star in a 2×2 rules out the cells outside it |
| Eight neighbors of a star | No touching, even diagonally, so the ring around a star is dots immediately |
| A full row | Once a row has its stars, its empty cells are dots. Auto dots does both of these for you |
| Three cells left in a row (one star) | The middle cell would leave both ends empty but blocked; if the two remaining cells are side by side, the cells that touch both are dots |
On two star boards count in bundles: one region means two stars, two rows mean four. If three regions fit entirely inside three rows, those regions use all six of the rows' stars, so every other cell in those rows is a dot. This counting trick is the heart of 10×10.
What are dots for?
A dot means no star can go here. Crossing out impossible cells shrinks the candidates until the star positions reveal themselves.
- Drag for many: drag from an empty cell and every empty cell you pass gets a dot. Start the drag on a dot and the dots you pass are erased instead.
- Auto dots: when on, placing a star dots its eight neighbors and the empty cells of any row, column or region that is now full. Undo removes them together with the star.
- Right click: on a computer, right click toggles a dot directly. On the keyboard it is X.
What help is there when I am stuck?
Check flashes any misplaced stars in red and tells you how many are wrong. Hint points out a wrong star if there is one, otherwise it places one correct star in the spot where the most surrounding cells are already decided.
Hints and undos are counted on the result screen. If you want a clean time, lean on Check and save Hint for emergencies. Touching stars and overfilled lines are always shown in red without pressing anything, and the small dots on the board frame show which rows and columns already have their full count.
What is the daily puzzle?
The daily puzzle is one 8×8 two star board per date, identical for everyone who opens it that day. It changes at midnight Korea time.
Finishing it records your time in the attendance log, and Share result makes a picture card with your time. On a normal board the share card carries a challenge link that opens the very same board, so a friend can race you on it.
Tips for faster solving
- Small regions first. A region of two or three cells has almost no choice, and it clears its whole row and column.
- Match rows to regions. If n regions fit inside n rows, the rest of those rows are dots. If n rows fit inside n regions, the cells of those regions outside the rows are dots.
- Dots before stars. Eliminating until one candidate remains is faster than guessing and undoing.
- Think in 2×2 squares. On a two star board a region that fits inside a 2×2 could hold only one star, which is impossible, so such a region must reach outside and its star is out there.
- Check once when stuck. Zero wrong stars means all your reasoning so far is sound, so carry on with confidence.
Controls
- Touch or mouse: tap a cell to cycle empty, star, dot. Drag from an empty cell to lay many dots, drag from a dot to erase. Right click is a dot.
- Keyboard: arrows or WASD choose a cell, Enter or Space for a star, X for a dot, Z undo, H hint, C check, Q toggles auto dots, Esc returns to the menu.
Your unfinished board, best times and the auto dots setting stay in this browser and are never sent to a server. The daily puzzle is not saved for Continue, so it is best finished in one sitting.