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What is a word ladder?
The rules, where the puzzle comes from, and how a four-letter ladder actually plays.
What a word ladder is
A word ladder is a chain of words of the same length, where each step changes exactly one letter. You start with one word, finish with another, and fill the rungs between them. Every rung must be a real word, so the chain reads as a list of English words rather than a row of near misses. The puzzle is also called a doublet. The aim is to get from the start word to the goal word in as few steps as you can.
The one-letter rule
Each step changes exactly one letter and leaves the other three where they are. You cannot add a letter, drop one, or swap two at the same time, and position matters. The chain COLD, CORD, CARD, WARD, WARM is a valid ladder: each rung is a real four-letter word, and each step moves a single position. A move that alters two positions at once is not a move, even when the result is a familiar word you would like to use.
The rule gives the puzzle its shape. Because each step touches one position, the letters you leave alone act as an anchor, and progress tends to happen one column at a time. When you are stuck, compare the start and goal and find the positions where they differ. Spend your moves on those positions. Changing a position that already matches tends to carry you further from the goal.
Why the rungs have to be real words
Requiring real words is what turns a letter game into a puzzle. Without that rule you could link any two words by writing nonsense in between, and there would be nothing to solve. Real words limit each rung to a small set of neighbours, and the set depends on which English words exist. Obscure words, dialect words and proper nouns are rejected, so a name that sits one letter away will not help you.
Lewis Carroll and APE to MAN
Lewis Carroll invented the word ladder in the 1870s. His original puzzle turned APE into MAN. That short example already holds everything the puzzle needs: a fixed word length, exactly one letter changed per step, and a real word at every rung. The same shape scales up to four letters. Four-letter ladders are usually easier and shorter than five-letter ones, because four-letter words have more neighbours than five-letter words.
One puzzle a day
Rung a Day publishes one puzzle a day, the same for everyone. It resets at local midnight, so the day turns over in your own timezone, and no account is needed. The word list holds about 2,300 common four-letter English words, with obscure words, dialect words and proper nouns rejected. Up to three hints are available, and a hint reveals one letter of a shortest route. Par is the number of steps in the shortest possible ladder, found by exhaustive search rather than estimated.
Questions
Does every rung have to be the same length?
Yes. Every rung matches the start and goal in length, and each step changes exactly one letter. A fixed length keeps the puzzle a search through a word graph rather than a free association exercise.
What does par mean?
Par is the number of steps in the shortest ladder between the two words, found by exhaustive search rather than estimated. It is the real minimum for that puzzle. Matching par is a good result, and going over it still solves the ladder.
Do I need an account to play?
No. Rung a Day needs no account, and the daily puzzle is the same for everyone. It resets at local midnight, and up to three hints are available if you want them.
Play today’s ladder → one puzzle a day, about two minutes.