Enter two points — or a chain of waypoints — and get the great-circle distance, the steaming time at your planned speed, and the bunkers it burns. The fuel figure follows the same cube law the fleet simulation uses. Nothing you type leaves the browser.
The shortest path over a sphere is a lower bound on the real passage. Routeing round land, canals and traffic separation always adds miles, so treat the great-circle number as a minimum and use the sea margin for the figure you actually plan on.
Consumption scales roughly with the cube of speed: cons = k·v³. Give one known point — a reference speed and its daily burn — and the tool scales it to your planned speed, then multiplies by the steaming days.
This is the same distance and fuel model behind the fleet simulation and the route planning inside MarOps.