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[INPUT]: Public game and tool guides and live About/Privacy/Contact pages.
[OUTPUT]: Self-contained key facts, product distinction (playable game vs custom grid solver), calculation rules, limitations and links for 4FunPuzzle.
[POS]: Root reading entry point; product details are synchronized with the public HTML guides.
[PROTOCOL]: 变更时更新此头部，然后检查 CLAUDE.md
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# 4FunPuzzle

> An independent puzzle website offering a free online Crossmath (Cross Math) game and a custom grid Solver for arithmetic crossword grid puzzles.

Consult the live pages for current information; this index does not describe planned products or an API.

## Play Crossmath Online (/crossmath/) — Key Facts

- **Product type**: Playable game with 60 built-in original puzzles (Easy 5×5 to Expert 11×11), each verified by a constraint solver to have exactly one solution. This is a preset-level game, distinct from the custom grid solver below.
- **Access & cost**: Free to play in the browser, with no account, login or app download.
- **Rules**: Standard order of operations (PEMDAS / BODMAS): multiplication and division before addition and subtraction (2 + 3 × 4 = 14, not 20). Hard and Expert tiers include chained equations (A = B = C), unknown result cells and duplicate number tiles.
- **Progress & privacy**: Session progress stays in page memory only; nothing about the game is written to browser storage or uploaded.

## Crossmath Solver (/crossmath-solver/) — Key Facts

- **Tool type**: Interactive custom grid solver (enter your own puzzle grid, fixed operators and remaining number tiles to calculate a solution on your device; not a pre-made puzzle game).
- **Access & cost**: Free to use in your browser, with no account, login or app download required.
- **Calculation rules**: Switchable between **Multiply / divide first** (standard order of operations, PEMDAS / BODMAS) and **All operations left to right** (sequential evaluation).
- **Supported grids & arithmetic**: Custom rectangular grids (including 5 × 5, 7 × 7, 11 × 11 and 13 × 13 layouts), Unused gap cells, shared crossing numbers, repeated tiles, zero and negative whole numbers (±), unknown result cells and exact fractional intermediate division.
- **Search budget & results**: Reports one unique answer, more than one answer, no answer fits, or search limit reached (default 3 seconds or 1,000,000 search nodes, extendable to 15 seconds).
- **Current limitations**: Screenshot upload and OCR are not currently supported. No official daily or level-number answer library, no step-by-step hint sequence, and no Kakuro, KenKen, star or letter rules.
- **Privacy**: Calculation runs locally on your device; puzzle grids and answers are not uploaded or saved to browser storage.

## Documentation and links

- [Play Crossmath Online](https://4funpuzzle.com/crossmath/): Canonical playable game page with built-in unique-solution puzzles.
- [Game guide](https://4funpuzzle.com/crossmath/index.md): Machine-readable companion generated from the public game guide.
- [Crossmath Solver](https://4funpuzzle.com/crossmath-solver/): Canonical interactive tool and public guide for custom grids.
- [Tool guide](https://4funpuzzle.com/crossmath-solver/index.md): Machine-readable companion generated from the public HTML guide.
- [About](https://4funpuzzle.com/about/): Project scope and independence from game publishers.
- [Privacy](https://4funpuzzle.com/privacy/): Local puzzle calculation, hosting and optional analytics.
- [Contact](https://4funpuzzle.com/contact/): Support and feedback.