Make a crossword for your class in ten minutes

What a word list needs before it can become a grid, how to write a clue with only one answer, and what to do with the word that will not fit.

You need two things before you open any tool: the words, and one clue for each of them. Six to twenty words is the size that behaves, which is also the size of the vocabulary list for one lesson. Below two words there is nothing to build, because a crossword is made of crossings and a single word crosses nothing.

The grid comes out of the words, not the other way round. There are no black squares here and no rotational symmetry; those belong to the newspaper crossword, which starts from a fixed grid and then hunts through a dictionary for words that fit it. Your grid is the smallest rectangle that holds whatever got placed, so it changes shape every time you change the list, and the cells nothing lands on are simply not printed.

A word can only be placed where it shares a letter with a word already in the grid, so a word that shares no letter with any of the others cannot be placed at all. Take CAT, DOG, FISH and LYNX: L, Y, N and X appear in none of the first three, so LYNX has nowhere to cross and stays out. This is not a limitation of the tool, it is what a crossword is, because a grid in two disconnected pieces cannot be solved as one puzzle.

When that happens the fix is in the list, and there are three of them. Change the form of the word, since LYNX has no home but LYNXES ends in the S of FISH; swap it for another word that means the same thing; or add one word that bridges, meaning a word that carries a letter of the orphan and a letter of everything else. The bridge is usually quickest, and it leaves you with one more clue rather than one fewer word.

A clue has to pick out one answer, not a category. Animal fits CAT, DOG and LYNX equally well, so it is not a clue, it is a heading; it purrs and sleeps all day fits exactly one word on that list. The grid does help, because the number of squares rules out most of the rest, but never lean on the letter count alone: the answer should still be the only one when the clue is read on its own.

Test a clue by reading it aloud to somebody who has not seen the list. If they offer two answers, the clue names a class of things rather than a thing, and the repair is to add the detail that only your answer has. This costs about fifteen seconds per clue, and it is the difference between a sheet the class finishes and a sheet you spend the lesson explaining.

Keep clues to one line. The printed sheet sets the clue lists in two columns under the grid, so a clue much over sixty characters wraps, and twenty wrapped clues push the grid down until it will not fit on the page with them. Short clues also number better, because a clue is read next to its number and a long one drifts away from it.

Two things happen silently, and both are worth knowing before you check the answer key. Accents are stripped, because an accented E would never cross a plain E and because nobody can write an accent into a square; spaces go too, so ICE CREAM occupies eight cells in a row while the clue list still prints it with the space. Repeated words are dropped, the first one and its clue kept. Read the answer key once, check that no word you meant to use is sitting in the list of words that could not be placed, then print page 1 for the class and page 2 for yourself.