# Lattice Swap

> A swap-the-letters word puzzle in the style of the daily word-lattice games that are trending in October 2026: six five-letter words cross on a 5x5 lattice (three across, three down, sharing nine tiles), every tile is shuffled, and you swap two tiles at a time until all six words read true - within par plus five swaps. Green means the right tile, yellow means the letter belongs elsewhere in a word through that tile, grey means neither.

URL: https://lattice-swap.skillsafe.ai/
API: https://lattice-swap.skillsafe.ai/api.html

## What runs free in the browser

- Daily lattice: one seeded puzzle per calendar day, the same for everyone, numbered from #1 (2026-10-18); no undo; streak, solved count and average stars kept in the browser.
- Practice: unlimited fresh boards with undo.
- Your own words: type five-letter words and the page builds a lattice from them, filling gaps with everyday words.
- Puzzle links: copy a link (the LS1... code rides in the URL fragment) and a friend who opens it plays the identical shuffled board; the bare code can also be pasted into "Play it".
- Share grid: the coloured 5x5 result as emoji squares plus stars - no letters, no spoilers.
- Exports: Markdown (answers only after the game ends) and JSON.

## How a board is made (lattice.js)

1. Build: backtracking fill of the six slots in the order top across, left down, middle down, right down, middle across, bottom across, over theme words first and a built-in list of about 1,700 common five-letter words; an upper bound on theme words placed prunes the search.
2. Shuffle: random swaps of unlike letters; the board is kept only if replaying a greedy solver from it takes exactly the target number of swaps (par), no word is left complete, and few tiles start green. Par is therefore a real, achievable path - every board is solvable.
3. Colour: a non-green tile is yellow when its letter is still needed at a non-green tile of one of the words running through it, counted per word.

## What the model does (metered, model gpt-terra)

- task "theme": for any theme, 20-30 words of exactly five letters with a clue each (at most 12 words, never containing the answer), a title and a blurb; easy clues are direct, tricky clues use fair misdirection. The page fits as many as it can into the crossings (typically 3-4 of 6) and fills the rest with everyday words. "New words, same theme" sends the previous words as `avoid`.

## What the page checks in every reply

Words that are not five plain letters, repeats, words it was asked to avoid, clues that contain their own answer (hidden), how many of the six lattice words came from the theme, and theme words outside the built-in list.

## Sources

- @gamedev-skills/puzzle - the puzzle-genre playbook: board model separate from the view, deterministic resolution, exact undo, seeded and solvable generated boards.
- Trend: the swap-to-solve daily word lattice format, named the fastest-growing daily puzzle format in October 2026 browser-game roundups, e.g. https://fastplaygames.com/best/best-trending-games-2026
- Lattice Swap is independent and not affiliated with any other puzzle.