The appliance leak detector kit provides for completely mechanical leak detection with a red flag notification. A channel with a spring within is accessible via a longitudinal division within a rear side. A pair of holes in the rear side provides a spring anchor. The spring is extended outwardly from one of a pair of slots in the front wide, and fastened to a flagpole with flag. Another slot of the pair of slots provides for the flag to be held within the channel by a liquid soluble adhesive until a moisture wicked by an absorbent material migrates to the adhesive. The moisture causes the flag to release and pop distally from a front side of the channel, wherein a user notices a leak. A pair of absorbent material projections provides for a pair of slats that are part of the kit to install a remainder of the kit.