Word Ladder Solver

Overview

A word ladder is a puzzle invented by Lewis Carroll in 1877: change one letter at a time to transform one word into another, with each intermediate step being a real word. The solver finds the shortest valid chain from your start word to your end word.

Word puzzle enthusiasts, classroom teachers using ladders to teach vocabulary and spelling, algorithm students implementing shortest-path search, and ARG designers building puzzles with multi-step transformations all reach for it. It's a delight to watch the solver find unexpected paths.

How it works

The solver models the problem as a graph: each English word of the same length as your start word is a node, and an edge connects two words if they differ in exactly one letter. Finding the shortest ladder is then a breadth-first search from start to end across this graph.

For 4- and 5-letter words the graph fits easily in memory and the search is near-instant. For longer words the graph grows and the search may take a moment. If no ladder exists (your start and end live in different connected components), the solver reports no solution.

Examples

Start:   COLD
End:     WARM
Ladder:  COLD → CORD → WORD → WARD → WARM

Start:   HEAD
End:     TAIL
Ladder:  HEAD → HEAL → TEAL → TELL → TALL → TAIL

Start:   PEN
End:     INK
Ladder:  PEN → PIN → PIE → DIE → DUE → DUO → DUN → ... (longer ladder exists)

FAQ

What if no ladder exists?

Some word pairs are in disconnected parts of the word graph — there's no path between them through real intermediate words. The solver reports this and you can try a different target.

Can I customize the dictionary?

The solver uses a built-in word list of common English. Variants for Scrabble dictionaries or for other languages would require swapping the underlying list.

Lewis Carroll invented this?

Yes. He called them "doublets" and published the rules in Vanity Fair in 1879. They've been a popular logic puzzle ever since.

Try Word Ladder Solver