Caloptilia alchimiella (commonly known as yellow-triangle slender) is a moth of the family Gracillariidae. It is found in Europe and the Near East.
The wingspan is . Forewings purplish - ferruginous; dorsum suffused with yellow towards base; a large triangular yellow median costal blotch, apex often rounded. Hindwings dark grey. .
The moth flies from May to July depending on the location.
The larvae feed on Quercus species, Castanea sativa and Fagus sylvatica.