Abstract: The invention is a gutter cap for ducting rainwater to a rainwater gutter, while simultaneously deflecting debris. The invention is particularly suitable for retrofitting pre-existing aluminum gutters. The gutter cap can be installed with minimum tools and with no disruption to the existing gutter. The gutter cap is comprised of a sloped cover, which uses the attraction of water to bend water around a hooked edge as it drains across the sloped cover and ducts it into the trough. The cover, which forms a roof over the gutter's trough, is mounted with mounting blocks that snap on the cross-struts supporting the gutter, and these mounting blocks interlocks with the hooked edge of the cover. An opposing longitudinal edge on the cover is attached to the fascia board of the roof using a few screws or nails.