Star Battle Puzzles

Common questions

How do you play Star Battle?

Place stars on a square grid that is split into outlined regions. Every row, every column and every region must hold exactly the chosen number of stars: one on any board here, or two on 8 × 8 to 10 × 10 boards when you choose two. No two stars may touch, not even at a corner, so stars at row 1, column 2 and row 2, column 3 are flagged as touching diagonally. Dots are your own reminders for cells that cannot hold a star; they never count toward finishing. The puzzle is solved as soon as every row, column and region holds its stars and none touch.

Does every puzzle have exactly one solution?

Yes. For each seed the generator lays out a random valid set of stars, grows one region around each star (for two stars it pairs neighbouring areas into regions) and checks whether another layout also fits. While one does, it moves a cell holding one of that layout's stars, with any part of the region it would cut off, into a neighbouring region, which rules the other layout out without disturbing the intended one. A separate solver that works cell by cell and does not know the intended answer must then prove exactly one solution within 200,000 steps before the puzzle is offered, and the page repeats that proof when the puzzle opens. A proof that reaches its step limit offers nothing: Generate from seed keeps the previous puzzle, and New puzzle moves on to the next seed, up to 16 seeds. Each seed may try up to 48 candidate layouts within 1,200,000 steps. Steps are counted, not timed, so the same seed builds the same puzzle on every device. Generation runs in a background worker that is stopped after eight seconds, keeping the previous puzzle; when workers are unavailable, the page generates the puzzle itself.

How do stars, dots, hints and undo work?

Choose Star, Dot or Clear, then tap a cell; tapping a star with Star, or a dot with Dot, removes it. Undo and redo step through every star, dot and clear change until the puzzle is solved; once every rule holds, the result is final, and Replay as practice starts the same puzzle again. Hint first turns a star that cannot be right into a dot, the selected cell first; when every star you placed is right, it places a star of the solution in the selected cell if that cell holds one, otherwise in the first missing cell in reading order. Reveal solution shows the answer while keeping your own marks underneath. Hint and Reveal solution turn the run into assisted practice. Rows, columns and regions with too many stars, or with too few unmarked cells left for the stars they still need, are flagged from the rules alone, never from the answer.

How is the Star Battle challenge scored?

The challenge is one seeded original 6 × 6 puzzle with one star per row, column and region. Score is 1000 minus your final retained star placements, never below 0, and higher is better. Every star you put on a cell is a placement, including a star put back after you removed it, so a clean solve places six stars and scores 994, the best possible. Dots, clears and taps that change nothing add no placement, and undo removes the undone placement. Hint, Reveal solution, an answer key printed before finishing, restored progress, replays and puzzles already opened in this browser, including rotated or reflected copies, stay practice. Scores are self-reported.

What happens when someone opens a challenge link?

The page shows the shared score, the fixed rules and a Start same challenge button; nothing starts on its own, and the button is disabled once the shared attempt starts. The link carries only the seed, the board size setting and the claimed score, never marks or the answer, and the board is regenerated from the seed. A challenge link with a fractional, out-of-range, duplicated or wrong-tool value is refused with a message, and ordinary practice opens instead. After a fresh unassisted solve you see both scores, the signed difference and whether you did better, tied or scored lower, with Copy challenge link, Share challenge and Download result card for a new link that carries your score for the same puzzle. Your earned score stays on the page when you replay or start another puzzle, until another scored solve replaces it.

Can I print a puzzle or come back to it later?

Print puzzle prints the empty region grid only, without your stars, dots or the solution. Print puzzle and answer key adds the stars on a separate page and, if you have not finished, turns the run into assisted practice. The print sheet leaves the page once printing ends. Once you make a change, progress is saved in this browser without the solution. On your next visit an unfinished puzzle reopens automatically, unless you arrive through a valid challenge link: it is regenerated from its seed and your history is replayed onto it, as practice. Every puzzle that opens is remembered in this browser right away, even one you never touch, so a reload cannot make it a fresh challenge. Saves keep up to 10,000 changes and remember up to 1,024 opened puzzles. If storage is unavailable, the puzzle stays playable in the open tab.

Can I play with a keyboard or on a phone?

Yes. Tap a cell to apply the chosen mark, or use the arrow keys and press S to place or remove a star, D or X to place or remove a dot, and Backspace or Delete to clear. Mark selected cell, the move buttons and a selected-cell list give the same control without a keyboard. Every cell is at least 44 pixels, and on narrow screens every button is too; larger boards scroll inside their own frame on a phone instead of shrinking the cells. Each cell's accessible name includes its row, column, region and mark, and the page lists every row, column and region with its star count, plus a text version of the board.