Most specs fail not because they're too short, but because they try to solve everything at once. The fastest way to a buildable MVP scope is to force every decision through one question: what is the smallest thing a real user will pay for, use, or sign up for?
We start with a single user and a single job. Write the one sentence that describes the outcome they're hiring your product to achieve. Everything that doesn't serve that sentence is, by definition, out of scope for version one.
From there the day has four moves: list every feature you can think of, score each against the core job, cut everything below the line, then cost what remains. The cutting is the work. A spec with fifteen features isn't a spec — it's a wishlist with a date on it.
The output you want by end of day is short on purpose: the core job, the must-have features, the three things you're deliberately not building, and a rough cost. That's enough to start. The rest you'll learn faster from a live product than from another week of planning.
