Criss-cross (word fill-in) book generator for Amazon KDP

What a criss-cross is, and the one way it goes wrong

A criss-cross (also sold as "word fill-in" or "fill-it-in") is a crossword-shaped grid with no clues: the words are listed by length, and the solver works out where each one goes from its length and from the letters where words cross. Unlike a crossword, there is nothing to know, only to fit.

The one way they go wrong: a grid where two words of the same length could swap places. Then there are two correct fills, the answer key at the back matches only one of them, and the reader who found the other one leaves the review. Puzzle Press solves every grid it builds with a backtracking solver that counts fills; if it finds a second, the longest word is printed into the grid as a starter, and if that still leaves two, the grid is thrown away and rebuilt. Every puzzle in every book has exactly one fill.

Grades

Words come from the same 90 themes as the word search books, or a list you paste. Each puzzle draws its own words, so a Halloween fill-in book is fifty different Halloween grids. Grids are trimmed to the shape the words make — no black squares, no padding — and the word list beneath is grouped by length.

Measured on 1,800 grids

On 22 October 2026 we built five grids at every grade from each of the 90 built-in themes, then solved every grid again from scratch. All 1,800 had exactly one fill. None needed the starter word: in this run, every layout that could be filled two ways still could with its longest word printed in, and was thrown away.

Most layouts are thrown away before the uniqueness check: the words would not all cross, or the grid formed a stray run of letters that is not on the list. When a theme cannot make a grid at the grade you asked for, the book drops that puzzle one grade rather than leave a gap. In whole 20-puzzle books, that happened to 209 of 1,800 Medium puzzles, in 20 of the 90 themes. The worst were short state lists (11 to 13 words): every Medium West Virginia puzzle came out Easy. Until this measurement it happened silently. Now each such puzzle is labelled with its real level, and the tool tells you how many there are, so you can paste in a longer list or choose the easier grade knowingly.

What a book costs to print, and earns

Page count is title, copyright, one puzzle per page, a divider, solutions 6 to a page, and four notes pages, rounded to an even number. Printing is KDP's flat rate up to 110 pages, then $1.00 plus 1.2¢ a page. Royalty calculator for other prices and trims.

The rules every KDP interior has to meet

Page size equal to the trim, margins that grow with the page count, fonts embedded, 24 to 828 pages and an even count, a cover whose spine width is page count × paper thickness with nothing added. The tool lays every book out to these; if you would rather know them yourself, they are all in the guide, with the numbers.