Rules
Shakashaka rules: In some empty cells, shade a right triangle occupying exactly half the cell. All unshaded area must be rectangular. A number in a cell indicates how many rectangles are in the up to four cells orthogonally adjacent to the clue. In other words, there are five possibilities for each empty cells: leaving it empty or one of the four right triangles: ◢, ◣, ◤, ◥.
Example
Here is an example of a shakashaka grid and its solution.
Online solve
In order to solve Shakashaka puzzle on Penpa, either use the shape mode, and find the triangles in shape, or use the shakashaka in the Paint section of the Composite mode. In this mode, a left click put a dot in a cell, and a click while dragging toward one of the cell corner put a triangle filling this corner.
For automatic solution checking, place correctly all rectangles.
History of Shakashaka
Shakashaka is a puzzle type developed and published by Nikoli.