This is an extensive database of yarn, easily searchable by yarn manufacturer, fiber, weight and type. They include past years yarns, making it easy to check if a yarn you like is discontinued. They’ll tell you weight, fiber composition, washing instructions, yardage per skein, texture (plied or not), and recommended needle size and gauge, as well as showing you a color card for the yarn with color names and numbers clearly labeled. Links to the yarn brand website and yarn manufacturers websites are provided.
In addition, you can bookmark yarns that you like for easy future reference.
It is an astounding useful resource, and I am thrilled to have found it.