The craft page takes any list of words and builds a sheet from it, which makes it useful for a spelling list, a unit vocabulary set, or a roster of names for the first day of a season.
It also has rules, and a list written without knowing them produces a disappointing sheet for reasons that are not visible on screen. Here is what the generator actually does with what you type.
Words under three letters are thrown away
This is the rule that surprises people, because a spelling list for five year
olds is full of two letter words. AT, IN, ON, IT, UP, GO.
None of them survive, and the reason is that they cannot work. Every cell in the
grid that is not part of a placed word gets a random letter. In a field of
random letters, any given two letter sequence turns up by accident many times
over on a normal sheet. A child asked to find AT finds it in a dozen places,
all but one of them by accident, and the exercise stops meaning anything.
Three letters is short enough that it can still happen occasionally, which is worth knowing if you are building a CVC word sheet. It is a reason to stay on the small grids for that kind of list, since a smaller grid has far fewer places for the accident to occur.
A word cannot be longer than the grid is wide
The grid is a square, so the longest word that fits on a 14x14 is fourteen letters. On an 8x8 it is eight.
This is enforced silently: words that do not fit are dropped from the sheet without a warning. If you paste twenty vocabulary words and only eleven appear, the missing nine were too long for the size you picked. Move up a size and they come back.
It bites hardest on lists of names.
State names are the clearest case, where
MASSACHUSETTS and NORTH CAROLINA are both thirteen letters once the space
comes out, so they need the largest grid to exist at all.
Each size holds a fixed number of words
Even if a hundred words fit, the sheet does not use a hundred. The cap is twelve words on the 8x8, sixteen on the 10x10, twenty on the 12x12 and twenty-five on the 14x14.
Give the generator more than the cap and it picks a subset at random, which is a feature rather than a limit: generate again and you get a different selection from the same list, so a class of thirty can have thirty sheets covering the same vocabulary without any two being identical.
Give it fewer than the cap and every word is used every time.
Spaces disappear
NEW YORK becomes NEWYORK. ICE CREAM becomes ICECREAM. A grid holds one
letter per cell and has nowhere to put a space, so multi word entries run
together.
Tell students before they start. A child who does not know it will look for a gap that is never there, decide the puzzle is broken, and be right to complain.
The same applies to anything that is not a letter. Apostrophes, hyphens and
accents are stripped, so O'BRIEN becomes OBRIEN and T-SHIRT becomes
TSHIRT.
What actually makes a list good
Beyond the mechanics, three things separate a list that produces a satisfying grid from one that does not.
Mixed lengths. A list where every word is four letters gives a grid that feels flat and finishes in two minutes. A list that runs from four letters to eleven gives the eye somewhere to go, and the long words act as landmarks that make the short ones easier to spot afterward.
Different first letters. Twenty words that all start with S is genuinely harder, but in the unrewarding way. The searcher cannot use their first move, which is sweeping for an initial letter, so every word becomes a full scan. Two or three shared initials are fine. Fifteen is a slog.
Words that share letters in the middle. This one is invisible and it is the difference between a good grid and a loose one. When words overlap, the grid knits together and the random filler has less room, which makes the puzzle denser and the finds more satisfying. A list built on a pattern does this for free, which is why compound words and word family lists produce better grids than a list of unrelated nouns.
A quick test before you print thirty
Generate the sheet, then hit New layout twice. If all three versions look reasonable, the list is fine. If words keep vanishing, they are too long for the size. If the grid looks sparse, the list is too short or too uniform, and adding five words with different shapes usually fixes it.