Ask the helper "how many bones to 77 Prayer?" or "how long to 99 Fishing?" and it works the answer out from the game's XP table rather than estimating. It walks the levels between where you are and where you want to be, picks the best training option at each one, and reports how many of each material that takes, how long it runs for, and how many you already hold in your bank and pack.
Two things it gets right that are easy to miss by hand. Best does not mean most obvious — Gargoyle Dust beats big bones on a gilded altar from Prayer 20, at the same speed. And options with requirements outside the skill are excluded until you meet them: a gilded altar needs a level 75 Construction house, so without one the plan trains around it and tells you what you are missing. Your account's XP rate is applied too, so a Grindman's answer is roughly double a normal account's.
Ask for the fewest items instead of the fastest route and it re-plans for the one you care about. Only skills trained by repeating an action can be costed this way — Farming, Slayer and the melee and ranged skills are trained by doing, not by repeating a recipe, and it says so rather than guessing. Magic counts, but its ladder starts at level 7: the levels below that come from casting in combat.