Every Puzzle Is Computer-Verified to Have Exactly One Solution
The most common complaint about auto-generated Star Battle puzzles is that some grids are ambiguous — they admit multiple solutions, and finishing them forces you to guess. We built this site the other way around: no puzzle is published unless a solver proves it has exactly one solution.
How the Verification Works
Each puzzle goes through a strict pipeline before it ever reaches your browser:
- Generation. An engine grows a grid partition — contiguous regions, balanced sizes, no degenerate slivers — and proposes a star layout for it.
- Exhaustive solving. A backtracking solver then enumerates every valid completion of that grid under the full rule set: row quotas, column quotas, region quotas, and the no-touching constraint including diagonals.
- The one-solution gate. Exactly one completion → the puzzle ships. Zero completions (a broken grid) or two or more (an ambiguous grid) → the puzzle is discarded, logged, and regenerated.
There is no sampling and no spot-checking — the solver runs on every daily puzzle and every practice grid on the site, including both the 8x8 one-star and 10x10 two-star formats.
Why Uniqueness Is the Whole Game
A logic puzzle is a promise: the clues you can see are sufficient to determine the answer. That promise only holds when the solution is unique. On a grid with two valid completions, deduction eventually runs dry — not because you missed something, but because the remaining ambiguity is real, and the only way forward is a coin flip.
Uniqueness is what makes technique-based solving honest. When the board looks stuck, there is always a deduction waiting to be found — never a guess you are forced to make. That is also why our solver can be authoritative: it computes the one true answer, not one of several.
Zero-Guessing, By Construction
Because every published grid passes the one-solution gate, every puzzle on this site is solvable start to finish with pure logic — neighbor marking, region counting, pigeonhole arguments, the full toolkit. Difficulty on this site means the deductions are deeper, never “the puzzle is ambiguous and you must bifurcate”. If you ever see a solver elsewhere recommend trial-and-error on one of our grids, treat it as a bug report: it would mean our gate failed, and we would want to hear about it via the contact page.
Difficulty Without Compromise
Hard puzzles are easy to make — just stop filtering. Hard puzzles that remain uniquely solvable are the actual engineering problem. Our daily series paces itself across the week: gentler grids to open, denser regions and tighter pigeonhole arithmetic toward the end. The difficulty curve changes, the guarantee never does.
The daily archives keep that promise retroactively too — every past puzzle in the archive passed the same gate on its release day.
Frequently Asked Questions
How do you verify that a puzzle has a unique solution?+
Every generated grid is fed to an exact backtracking solver that enumerates all valid completions. The puzzle is only published if the solver finds exactly one. If a grid has zero solutions or more than one, it is discarded and never reaches the site.
Are the puzzles hand-made or generated?+
They are generated by our engine and then filtered by the uniqueness solver, which combines the scale of automated publishing with a quality guarantee hand-made puzzles cannot offer across thousands of grids.
What does "logically solvable" actually mean?+
It means there is a chain of logical deductions — neighbor eliminations, region counting, pigeonhole arguments — that determines every star without ever testing a hypothesis. A puzzle with multiple solutions cannot guarantee this, which is why uniqueness is the line we refuse to cross.
Play a Verified Puzzle Now
One guaranteed-solvable grid every day, plus practice formats and a printable archive.