Linear
Click and drag to set the gradient direction. The drag defines the transition from the start color to the end color.
The Gradient tool paints a smooth transition between your current foreground and background colors on the canvas.
You can activate the Gradient tool from the canvas toolbar.
Gradient only draws into the active raster layer:
If a raster layer is not selected, the tool is unavailable.
The Gradient tool uses the current FG/BG color pair:
Linear
Click and drag to set the gradient direction. The drag defines the transition from the start color to the end color.
Radial
Click to place the center, then drag outward to set the radius. The gradient fades from the start color at the center to the end color toward the outside.
The toolbar includes a Clip Gradient toggle:
In practice:
The Gradient tool is a raster-only canvas tool for painting linear and radial color transitions. Use it when you want soft blends between your FG and BG colors, and use Clip Gradient to decide whether the effect stays local or fills the full bbox.