About sudokuprint.app

What this site is

sudokuprint.app is a free sudoku generator for people who like to solve on paper. It makes new puzzles at four levels, for kids and in large print, and turns them into pages you can print or save as PDF. It is published by Takreparation Skåne AB in Ängelholm, Sweden.

How puzzles are made

1. A complete, valid 9×9 grid is built at random with a backtracking search.
2. Numbers are removed in pairs that mirror each other through the center, which gives the familiar symmetric look.
3. After every removal, a solver counts the solutions and stops at two. A removal that allows a second solution is undone.
4. A grader solves the puzzle the way a person would and records the hardest technique needed. Only puzzles that match the chosen level are kept.

Every step is driven by a seed from the puzzle code, so the same code always gives the same puzzle.

How we test it

Before launch we generated 1000 puzzles per level and checked each one automatically: exactly one solution, a valid answer, every clue matching the answer, the grade matching the level, and the code rebuilding the same puzzle. All of them passed. The kids grids were tested the same way.

No account, no tracking

There is nothing to sign up for. The site counts page views with Cloudflare Web Analytics, which uses no cookies. See the privacy page for details.