Google Flights allows you to track the price of flights to a destination (with given departure and return dates), and alerts you when this price drops for any of the possible flight options for the route.
I am looking for a more general app or website, where you can track the price of flights to a particular destination, with a given duration of the stay (plus/minus some days), but without a fixed date departure date. That is, since I can decide when to take vacations at work, my major constraint at the moment is the price of the flight. So I'll take tickets for the dates where the prices drop and that's the kind of alert I would like to setup.
I want to receive an alert whenever the prices for such any flight to said destination might become cheap.
I have checked skyscanner and similar sites, but none seem to offer this precise functionality.