Star Battle solving techniques
These are the deductions our solver uses, from the first rule you learn to the contradiction that only Expert grids need. Each one shows a real step from one of our puzzles, and how often our bank needs it at each level.
- Stars never touch
- Full row, column or region
- Last cells left
- Region inside one line
- A star here leaves no room
- N regions in N lines
- 2x2 blocks
- Two-line squeeze
- Short chain
- Contradiction
Stars never touchtier 1
When: Every cell around a star is empty, diagonals included.
The rule that makes Star Battle a puzzle. As soon as a star is placed, its eight neighbours are out, and those dots often finish a row or region for you.
From one of our puzzles (8x8 1-star): Stars never touch, not even diagonally, so the 3 open cells around the star at C8 are empty.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| Stars never touch | 100% | 100% | 100% | 100% |
Full row, column or regiontier 1
When: A unit that already has its stars is empty everywhere else.
A row, column or region that has all its stars is closed: every other cell in it is empty. In 2-star grids this fires only after the second star.
From one of our puzzles (8x8 1-star): Row 8 already has its star, so its other open cells are empty.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| Full row, column or region | 100% | 100% | 100% | 100% |
Last cells lefttier 1
When: A unit with exactly as many open cells as missing stars takes a star in each.
When the free cells of a unit are exactly as many as the stars it still needs, they all take stars. In 1-star grids this is the classic last free cell.
From one of our puzzles (8x8 1-star): The region with B6 needs 1 more star and has exactly 1 open cell left: C8.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| Last cells left | 100% | 100% | 100% | 100% |
Region inside one linetier 2
When: A region that fits in one row or column takes that line's stars; the rest of the line is empty.
A region whose free cells all lie in one row must take that row's star, so the row is empty outside the region. The same works with columns, and the other way round: a row whose free cells sit in one region.
From one of our puzzles (8x8 1-star): The region with A4 fits inside column A, so it takes the star of that line; the other 5 open cells there are empty.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| Region inside one line | 0% | 99% | 87% | 66% |
A star here leaves no roomtier 2
When: A cell is empty when a star in it would leave some row, column or region without room.
Try a star in a cell in your head: its neighbours go dark. If that would leave some row, column or region with no room for its star, the cell is empty. A two-cell region wipes out the cells that touch both of its cells this way.
From one of our puzzles (10x10 2-star): A star at B1 would leave the region with A1 without room for its stars, so B1 is empty.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| A star here leaves no room | 0% | 75% | 100% | 100% |
N regions in N linestier 3
When: When N regions fit inside N rows (or columns), those rows hold no other stars.
Two regions that together fit inside two rows take both rows' stars, so nothing else in those rows can be a star. With three regions and three rows it is the same count; columns work too.
From one of our puzzles (8x8 1-star): The 3 regions with F1, G3 and H7 fit inside columns F, G and H, so they take all 3 stars of those lines; the other open cell there is empty.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| N regions in N lines | 0% | 0% | 91% | 72% |
2x2 blockstier 3
When: Two neighbouring lines split into 2x2 blocks; each block holds at most one star.
Cut two neighbouring rows into 2x2 blocks: a block can hold one star at most. If the rows need as many stars as there are blocks left, every block gets exactly one, and cells touching a whole block are empty. The same idea covers a unit whose free cells fit inside two 2x2 blocks.
From one of our puzzles (10x10 2-star): Columns F-G need 4 stars and split into 5 blocks that hold one star at most; only 4 blocks can still take one, so each does. The block at G2 has a star, and H2 touches all of it.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| 2x2 blocks | 0% | 0% | 25% | 56% |
Two-line squeezetier 3
When: A star here would leave two neighbouring lines too few 2x2 blocks for their stars.
The squeeze, measured with 2x2 blocks: a star here would leave a pair of rows or columns with fewer usable blocks than stars still to place.
From one of our puzzles (10x10 2-star): A star at E5 would leave columns C-D room for only 3 of their 4 stars (one per 2x2 block), so E5 is empty.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| Two-line squeeze | 0% | 0% | 21% | 58% |
Short chaintier 3
When: A star here forces a few placements by the basic rules alone, and they run into a dead end.
Place a star in your head and follow only the basic rules for a few moves. If they run into a wall, the cell is empty. This is the gentlest kind of contradiction, and we count it as a Hard technique.
From one of our puzzles (10x10 2-star): A star at D7 forces a short chain of placements by the basic rules, after which the region with A8 would be left without room for its 2 stars. So D7 is empty.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| Short chain | 0% | 0% | 36% | 99% |
Contradictiontier 4
When: If a star here forces a dead end a few moves later, the cell is empty.
The last resort, and the mark of an Expert grid: assume a star (or an empty cell), use every technique above, and reach a broken rule. The opposite must be true. Our hints say which rule breaks, so you can check it yourself.
From one of our puzzles (10x10 2-star): Suppose F1 were a star: following the rules from there, columns D-E would have room for only 3 of their 4 stars. So F1 is empty.
| Share of puzzles that need it | Easy (662) | Medium (662) | Hard (1,224) | Expert (562) |
|---|---|---|---|---|
| Contradiction | 0% | 0% | 0% | 100% |
Source: the Gridaday bank, 3,110 puzzles of Star Battle graded by our solver; data as of 2026-10-17.