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Word ladder rules
The precise rules, and the arguments people actually have about them.
The six rules, stated plainly
Rule one: every word has the same length as the start and the goal. Rule two: each step changes exactly one letter and leaves the other positions untouched. Rule three: every intermediate word must be a real word, not an abbreviation, a name or a plausible-looking string. Rule four: the change happens in place, so letter order is fixed. Rule five: a repeated word is not forbidden, but it never belongs to a shortest route. Rule six: the ladder ends at the goal, and the number that matters is your step count.
An anagram is a different word
An anagram uses the same letters in a different order, and steps are counted by position, so an anagram is not a step. TEAM and TAME share the T but reorder the other three letters, which is three changed positions. The test is mechanical: compare each position and count the mismatches. One mismatch is a legal step, zero means you typed the same word twice, and two or more means you changed too much. Lewis Carroll's original doublet turned APE into MAN one position at a time.
Names, dialect words and the dictionary problem
There is no single official dictionary of English, and ladders inherit that problem. One dictionary lists a word, another omits it, and a third marks it archaic or regional. Two players can disagree about a word without either being careless. The workable answer is one agreed list. Rung a Day uses a list of about 2,300 common four-letter English words, and rejects obscure words, dialect words and proper nouns. Proper nouns are the sticking point, since a surname or town can look like a four-letter word. The test is meaning: a proper noun names a particular thing, while a ladder word must mean something by itself.
Agreeing on a list does not end every disagreement, but it turns the argument into a lookup. Par works the same way. It is the number of steps in the shortest possible ladder, found by exhaustive search rather than estimated, so a claim about a shortest route can be checked. A word that is not on the list cannot shorten a route, and a route that needs an off-list word is not a route.
Reusing a word costs you steps
Nothing in a ladder forbids reusing a word, and nothing rewards it. If a ladder visits the same word twice, the rungs between the visits form a loop, and deleting the loop leaves a shorter ladder from the same start to the same goal. A repeated word therefore cannot appear in a shortest route. It can appear in your attempt, where it costs steps. If you are about to type a word you have already written, the word you need is somewhere else.
How to check a ladder
Check three things before you accept a ladder. Line the words up and confirm that every neighbouring pair differs in exactly one position. Confirm that no rung is a different length from the start, since one wrong-length word breaks the chain. Confirm that no word appears twice. If you are stuck, a hint reveals one letter of a shortest route, and up to three hints are available. Rung a Day sets one puzzle a day, the same for everyone, resetting at local midnight, so tomorrow brings a different ladder.
Questions
Does a ladder have to use four-letter words?
No. Every word only has to match the length of the start and the goal, so five-letter ladders follow the same rules. Four-letter ladders are usually easier because the graph is denser.
Can I use a word twice if it helps?
A repeat cannot help. The words between the first and second use form a loop, and removing it leaves a shorter ladder with the same endpoints. A repeat can appear in an attempt, but not in a shortest route.
What if a word is in my dictionary but not accepted?
That is the dictionary disagreement problem. Different dictionaries include different words, so a puzzle uses one agreed list. A word outside it does not count, however familiar it is.
Play today’s ladder → one puzzle a day, about two minutes.