One square at a time.

Yes. Every board in the library is checked for a unique solution in both classic and color mode, then rated by the solving techniques it needs. The engine verifies the puzzle again when you open it.

Numbers beside rows and above columns give the lengths of filled runs, in order. For example, 3 then 2 means a run of three cells followed by a run of two. In classic puzzles, leave at least one empty cell between runs.

Each clue gives a run’s length and ink color. Two consecutive runs of the same color need an empty cell between them. Different colors may touch. Online, you can also show color letters on clues and filled cells.

Yes. Play with fill and empty marks, undo, redo, and explanatory hints. Switch to Worksheet or Answer key to preview either side. Download a 300 DPI PNG or a PDF in Letter or A4. Your play marks do not appear on the blank worksheet.

Yes. Sign in and click Save progress while you play or view the worksheet. My puzzles keeps your marks and completed designs so you can continue on another device. Your first five saved puzzles are free; Plus includes unlimited saves. Updating or resuming an existing save stays available after membership ends. You can also submit a saved puzzle for community review.