Interactive Sudoku Solver

To set a value, select a cell and type a number.

To add a multi-cell constraint, select and drag; or shift-click.

To add a Little Killer constraint, select a diagonal arrow outside the grid.

To add a Sandwich , X-Sum , or Skyscraper constraint, select a row/column arrow outside the grid.

OR (Source)
OR

Auto-solve

Stats by runtime

Constraints

Create from selection

Global constraints

Layout constraints