Bridge two words by changing a single letter at a time, and every rung along the way must be a real word.
You're given a start word and a target word of the same length. Build a chain of words from one to the other, where each step differs from the one above it by exactly one letter and is itself a valid dictionary word.
The word ladder has an unusually well-documented birthday. Lewis Carroll said he invented it on Christmas Day 1877, devising it for two children, Julia and Ethel Arnold; his diary first mentions it on 12 March 1878, under the name Word-links, as a game for two players.
He published it as Doublets in Vanity Fair from the issue of 29 March 1879, with a book following from Macmillan later the same year. Others took it up — J. E. Surrick and L. M. Conant issued a collection called Laddergrams in 1927.
Its best-known appearance is in fiction. Vladimir Nabokov called it "word golf" in Pale Fire, where the narrator boasts of his records: "hate—love in three, lass—male in four, and live—dead in five (with lend in the middle)."
Word Ladder is a modern take on the classic letter-chain word puzzle, a traditional pen-and-paper game. This is an original, free browser version with daily challenges, difficulty levels and an optimal-move par to beat.