About Sudoku Builder

Sudoku Builder is a free, no-sign-up Sudoku game. Generate random puzzles across four difficulty levels, or use the builder to design your own board and share it with anyone via a single link.

Stored in the link

Every custom puzzle is encoded directly into its URL. We don't run a database and we don't need an account — when you copy a share link, the entire board travels inside it. Whoever opens the link gets exactly the puzzle you built.

Tools for solving

The player includes pencil notes, an auto-candidate mode that fills in every cell's legal digits for you, automatic note cleanup when you place a number, mistake highlighting, hints, and a timer. Choose from several themes — including a dark mode with blue notes, a classic light look, and a high-contrast option.

How puzzles are generated

Random puzzles start from a fully solved grid. Clues are then removed while ensuring the puzzle keeps a single unique solution, so every generated board is fair and solvable by logic alone.