Word Ladder — Change One Letter at a Time
Transform the start word into the target word by changing one letter per step.
How to play
- Change exactly one letter of the current word to make a new word.
- Type your next word and click Step (or press Enter).
- Repeat until you reach the target word shown in green.
- Use Undo if you go down a dead end.
- The puzzle pair is random each game — try to find the shortest path!
Transform the start word into the target word, changing exactly one letter per step. Every intermediate word must be a valid change. How few steps can you do it in?
How it works
Word Ladder is a word puzzle invented by Lewis Carroll in 1877. You are given a start word and a target word of the same length. Your task is to transform the start word into the target by changing exactly one letter at a time, with every intermediate step also being a valid English word.
For example, transforming CAT into DOG might proceed: CAT to COT (change A to O), COT to COG (change T to G), COG to DOG (change C to D). Each step changes one letter and produces a real word. The challenge is to find a valid path without creating a dead end where no single-letter change produces a real word.
Effective strategy involves working from both ends simultaneously: find words one step from the start and words one step from the target, looking for overlaps in the middle. This bidirectional approach often reveals shorter paths than working linearly from start to finish.
Word Ladder exercises vocabulary depth, lateral thinking, and the ability to hold multiple word states in mind simultaneously. It is a classic puzzle for language lovers and appears frequently in puzzle books and word game competitions.
Worked example
Solving a four-step ladder: COLD to WARM
- Start: COLD. Change one letter to get a valid word: CORD (D becomes R).
- From CORD, change one letter: WORD (C becomes W).
- From WORD, change one letter: WARD (O becomes A).
- From WARD, change one letter: WARM (D becomes M).
- Ladder complete in four steps: COLD, CORD, WORD, WARD, WARM.
COLD transformed to WARM in four valid steps.
Common mistakes to avoid
- Changing a letter to produce a string that looks like a word but is not in the standard dictionary, invalidating that step.
- Working only forward from the start and getting locked in a word cluster far from the target with no bridge available.
- Forgetting to keep track of words already used, which can lead to circular paths that revisit the same rungs without making progress.
Key terms
- Rung
- A single intermediate word in the word ladder, one step removed from the word above and below it.
- Dead end
- A word in the ladder from which no single-letter change produces another valid English word that continues toward the target.
- Bidirectional search
- A solving strategy that works toward the middle from both the start word and the target word simultaneously to find shorter paths.
Frequently asked questions
- Can I change any letter?
- Yes — change any single letter position to a different letter, one step at a time.
- Do I need to use real words?
- The game accepts any letter string (one letter changed per step) — focus on reaching the target.