Every SaaS founder building an MVP solo faces the same tension: move fast enough to find out if the idea works, without accumulating so much undocumented debt that the next six months of iteration become miserable. Spec-driven development sounds like it trades one for the other. In practice, the tier system is specifically built to avoid that trade.
Most of an MVP is light tier, and that's fine
The bulk of early SaaS work — auth flows, a settings page, a billing integration, a dashboard view — is light tier: one plan document, a focused test script, done. You're not writing EARS-format requirements for a toggle. The workflow's default cost is genuinely low, which is exactly what an MVP timeline needs.
Where founders actually get burned
The place solo founders get hurt isn't feature velocity — it's the handful of decisions that quietly become architectural without anyone noticing: the first version of the data model, the choice of how multi-tenancy works, the first real external integration. These are exactly the changes SpecDevShip's tier decision is built to catch, because they match its full-tier criteria (new subsystem, real migration risk) regardless of how small they felt when you started typing.
Product identity, written down once
product-design is worth running even at MVP stage, before the first feature spec — not as ceremony, but because "what is this actually for, and for whom" is the single most expensive thing to get vague and then have to untangle later, once three months of feature decisions have been made against an unstated assumption about your audience. Writing it down once, as a structured dialogue rather than a document you draft alone, catches the vague spots while they're still cheap to fix.
The real payoff: investor and cofounder conversations
A byproduct that matters more than it sounds: when you're raising, or bringing on a cofounder or first engineer, having an actual product.md and a handful of approved specs is a materially different conversation than "it's mostly in my head." You're not writing documentation for its own sake — you're building the exact artifact a due-diligence process or a new technical cofounder would otherwise have to extract from you in a dozen meetings.
Solo MVP building doesn't need heavier process. It needs the discipline to stay light on what's actually light, and catch the handful of decisions that aren't — before they've already shaped six other things.