Logic Puzzle Lab is a small independent puzzle studio. We make logic puzzles for adults who enjoy a real problem: killer, samurai and jigsaw sudoku, nonograms, kakuro, calcudoku and logic grid puzzles. Everything is free to play in the browser and free to print for personal and classroom use.
The site exists to offer puzzles you can trust. Too many puzzles online have a second solution hiding in the last few cells, or a hard label that really means long. Every page here is built to avoid both.
How the puzzles are made
Every puzzle is generated by our own software. A separate solver then checks it exhaustively and proves it has exactly one solution. If it finds a second one, the puzzle is discarded.
The nonogram pictures are drawn by us as pixel art, one square at a time, and each is checked the same way before it is used. The logic grid stories, settings and names are also our own.
How levels are set
Difficulty here is about technique, not clue counts. Our grader solves each puzzle step by step the way a person would, always trying the cheapest technique first, and the level is the hardest technique it needed along the way. A puzzle that can't be finished by logic alone, without guessing, is thrown away.
So an easy puzzle and an expert one differ in kind, and not just in length. Each puzzle type's page lists the techniques its levels call for, from cage combinations and singles up to wings and fish in killer sudoku, and from counting up to a single probe in nonograms.
Play first, then print
Every puzzle page follows the same pattern. The board is at the top so you can start straight away, and a Print PDF button gives you the same puzzle on paper with the answer on the last page. Large print editions are there for anyone who finds standard puzzle grids hard to read. You can browse the whole range on the all puzzles page.
Mistakes and suggestions
We check carefully, but if you find something wrong, such as a clue that doesn't match its answer, a typo in a story or a page that misbehaves, please tell us through the contact page. Error reports are the most useful messages we get. Notes on what makes the site harder to use are welcome too; our accessibility page explains what we've done so far and what is still on the list.