---
title: "Word ladders: API"
package: "@phaser-ae/word-ladder"
tier: Pro
version: 3.0.0-0
released: 2026-10-21
updated: 2026-10-21
description: "Turns one word into another a letter at a time, every step a real word, with seeded puzzles of a chosen length and par, hints and a solver."
url: https://phaser.io/packs/word-ladder/api
site: Phaser - https://phaser.io
---

# Word ladders: API

`@phaser-ae/word-ladder` — Turn one word into another a letter at a time, every step a real word, with seeded puzzles of a chosen length, par, hints and a solver.

## The pack

### `wordLadder`

```ts
function wordLadder(): Pack<{ wordLadder: WordLadderApi }>
```

The `word-ladder` pack: word ladder puzzles over the english-words lists. Pure logic, so it runs headless.

## Helpers

### `createWordLadder`

```ts
function createWordLadder(options: WordLadderOptions): WordLadder
```

Make a ladder: a generated puzzle from `seed`, or the one `start` and `goal` set. Throws a RangeError for options out
of range: a set word not in the list or not reachable, a step range with no puzzle in it, a limit below par.

### `ladderNeighbours`

```ts
function ladderNeighbours(word: string, words: WordList = englishLexicon(), moves: LadderMoves = 'change'): string[]
```

Every word one step from `word` in `words` (default the English lexicon) under `moves` (default `'change'`): one
letter changed, or with `'edit'` also one added or taken away. Shortest first, then alphabetical; `word` itself is
left out, and it need not be in the list. Empty for anything but letters.

### `solveLadder`

```ts
function solveLadder(start: string, goal: string, words: WordList = englishLexicon(), moves: LadderMoves = 'change', avoid: Iterable<string> = []): string[] | null
```

A shortest ladder from `start` to `goal` in `words` (default the English lexicon) under `moves` (default `'change'`),
both ends included, never through a word in `avoid`; null when there is none. Ties go to the alphabetically first
words, so the answer is always the same. Neither end need be in the list.

## Types

### `LadderMoves`

```ts
type LadderMoves = 'change' | 'edit'
```

What one step may do: `'change'` one letter (the length stays), or `'edit'`: change, add or take away one letter.

### `LadderRung`

```ts
interface LadderRung
```

One word on the ladder, and where it changed.

- `readonly word: string` — The word, lower case.
- `readonly changed: ReadonlyArray<number>` — The positions in `word` that differ from the rung before: the changed letter, or an added one. Empty for the start word and for a step that took a letter away.

### `StepResult`

```ts
interface StepResult
```

What a step did.

- `readonly rung: LadderRung` — The rung it added.
- `readonly phase: WordLadderView['phase']` — The phase after it.
- `readonly remaining: number | null` — The fewest steps left to the goal from the new word, or null when there is no way.

### `WordLadder`

```ts
interface WordLadder
```

A word ladder. Make one with `createWordLadder`.

- `observation(): WordLadderView` — The ladder as it stands.
- `check(word: string): { readonly ok: true } | Refusal` — Would a step to `word` be accepted now? `{ ok: true }`, or the refusal with a reason a player could be shown. Changes nothing.
- `step(word: string): { readonly ok: true; readonly result: StepResult } | Refusal` — Step to `word`. Refused, changing nothing, when `check` would refuse it.
- `undo(): boolean` — Take back the last step. False when there is none.
- `hint(): { readonly word: string | null; readonly remaining: number | null; readonly reason: string }` — The next word on a shortest way from the last word to the goal, not using a word on the ladder again; null when there is none or the ladder is over.
- `autoStep(): { readonly ok: true; readonly result: StepResult } | Refusal` — Play `hint()`'s word. Refused when there is none.
- `solve(from?: string): string[] | null` — A shortest ladder to the goal, as words with both ends: from the last word avoiding the words already on the ladder (no argument), or from any word in the list (`from`). Null when there is no way.
- `snapshot(): HistorySave<WordLadderMove>` — The ladder as a save: the seed and the steps. Restore it into a ladder made with the same options.
- `restore(save: HistorySave<WordLadderMove> | string): void` — Replace this ladder's steps with a save. Throws, changing nothing, when the save does not replay.

### `WordLadderApi`

```ts
type WordLadderApi = typeof rules
```

`game.wordLadder`: every function and type this pack carries, as one namespace.

### `WordLadderMove`

```ts
type WordLadderMove = { … }
```

A move: one step to a word.

- `readonly kind: 'step'`
- `readonly word: string`

### `WordLadderOptions`

```ts
interface WordLadderOptions
```

How a ladder is set up. Only `seed` is required; the default is a four-letter puzzle of 3 to 6 steps.

- `seed: number` — Picks the puzzle when `start` and `goal` do not set it, as an unsigned 32-bit integer.
- `length?: number` — Letters in a generated puzzle's start and goal. Default 4, or the length of `start`.
- `minSteps?: number` — Fewest steps the shortest ladder of a generated puzzle may take. Default 3.
- `maxSteps?: number` — Most steps the shortest ladder of a generated puzzle may take. Default 6.
- `start?: string` — The start word of a set puzzle; give `goal` with it. Must be in the word list.
- `goal?: string` — The goal word of a set puzzle; give `start` with it. Must be in the word list and reachable.
- `words?: WordList` — The words a step may be. Default the English lexicon.
- `moves?: LadderMoves` — What one step may do. Default `'change'`.
- `limit?: number` — Most steps allowed before the ladder is lost: a whole number no smaller than the puzzle's par, or Infinity (the default).
- `attempts?: number` — Start words tried when generating. Default 60.

### `WordLadderView`

```ts
interface WordLadderView
```

The ladder as it stands.

- `readonly phase: 'playing' | 'won' | 'lost'` — `'playing'`, `'won'` (the goal is reached) or `'lost'` (the step limit is used up).
- `readonly start: string` — The start word.
- `readonly goal: string` — The goal word.
- `readonly rungs: ReadonlyArray<LadderRung>` — Every word so far, the start first.
- `readonly par: number` — The fewest steps from the start to the goal.
- `readonly remaining: number | null` — The fewest steps from the last word to the goal without using a word on the ladder again; null when there is no way. 0 once won.
- `readonly steps: number` — Steps taken.
- `readonly limit: number` — Most steps allowed; Infinity for no limit.
- `readonly moves: LadderMoves` — What one step may do.

---

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