About Sudoku Knacker

Who We Are

Sudoku Knacker is an independent web project run by a small team of puzzle lovers and developers. "Knacker" is German slang for someone who cracks a tough problem — which is exactly what this site helps you do: knacken (crack) any Sudoku that stands in your way.

The project started with a simple frustration: most online Sudoku solvers are slow, cluttered with pop-ups, or quietly upload your puzzle data to a server. We wanted the opposite — a tool that loads instantly, solves instantly, and keeps your data on your own device.

What We Build

Today, Sudoku Knacker offers four core tools, all free and all running entirely in your browser:

• Sudoku Solver — enter a puzzle by hand or upload a photo, and get the solution (or a single-cell hint) in milliseconds.
• Play Mode — freshly generated puzzles from easy to expert, each verified to have exactly one solution, with notes, a timer, and mistake tracking.
• Printable Puzzles — print-ready puzzle sheets with optional answer keys, for the pencil-and-paper tradition.
• Techniques Guide — illustrated explanations of every essential solving technique, from cross-hatching to X-Wings.

How the Site Works

There is no Sudoku Knacker server doing any puzzle math. The solver engine, the puzzle generator, and even the photo recognition (OCR) that reads digits from your pictures are implemented in JavaScript and WebAssembly that run on your device. When you upload a photo of a newspaper puzzle, the image never leaves your browser.

Puzzle progress and preferences (like your light/dark theme choice) are stored locally in your browser's own storage — not in a database on our side. Clear your browser data, and everything we "know" about you is gone.

How the Site Is Funded

Sudoku Knacker is free to use, with no accounts and no premium tiers. The site is supported by unobtrusive advertising. We keep ads limited and clearly separated from content — if you'd like the details of how advertising cookies work, see our Privacy Policy.

Our Promise

• Free forever. Every tool on this site is free to use, with no usage caps.
• No accounts. No sign-up walls between you and the grid.
• Private by design. Your puzzles and photos stay on your device.
• Fast. The solver typically answers in under 10 milliseconds — even the average puzzle generation takes just a few.

Get in Touch

Found a bug, have an idea for a feature, or want to tell us about a puzzle that stumped our solver? We'd love to hear from you — head over to the contact page.