A closer look at Shade Link
Three conditions for a finished board
Every number starts unshaded. Shade some cells so each row and column has no repeated unshaded number. The remaining cells need not contain every number from 1 to 4. No two shaded cells may share a horizontal or vertical side; corner contact is allowed. All unshaded cells must form one group using horizontal or vertical steps. A diagonal step does not connect them.
A toggle edits one cell
Click or tap any number to switch its shaded state; its number stays visible but is crossed out when excluded. The label and pressed state give the same information without relying on colour. Each accepted toggle counts once, including toggling a shaded cell back. The interface allows wrong assumptions so you can inspect and undo them. It does not automatically identify a correct cell.
Check, recover and retry
Check shading reports equal-number pairs, shaded side pairs and unshaded groups. A win requires0 pairs of each kind and1 unshaded group. Checking adds no toggle and the board locks only after a successful check. Undo last toggle restores the previous shading, including after a win. Retry this board clears shading and history with unchanged numbers. Load beginner board restores the exact teaching example; its practice address reloads those numbers after refresh. New puzzle moves through 7 prepared boards, then repeats; it clears the practice address.
Accessible untimed play
Tab reaches cell buttons, Enter or Space toggles them, and arrow keys move focus to side neighbours without wrapping at a boundary. There is no countdown, account, payment, stored score or advertisement reward. Your choices stay in the current browser tab. The common mechanic follows Hitori rules described by Nikoli; these clue arrangements and code are original work for this site, with no affiliation or invention claim.
Common questions
Does a shaded number still create a duplicate?
No. Only unshaded numbers count in the row and column checks. Shading does not change the printed value.
May shaded corners touch?
Yes. The restriction applies to shared sides. However, diagonal shading can still trap an unshaded cell, so the connectivity rule must be checked separately.
Must I shade a fixed number of cells?
No fixed count is part of the rule. Finish when all three conditions hold; a low toggle count or fewer duplicates alone is not a win.
Does this improve my health or measured ability?
No such result is promised. This is an untimed logic exercise with explanations of the implemented rules.