Keepa

Keepa draws a price-history chart directly into Amazon product pages and can alert you when a price falls to a level you set. With 4,000,000 Chrome Web Store users and 4.7 stars from 5,100 ratings it is the most-installed tool of its kind. It is something you consult before you buy rather than a checkout actor, which is why it belongs in a different layer of a deals stack from any cashback extension.