The one-sentence test
Can a real user complete the single most important workflow, start to finish, without it? If yes, it's not core — it can wait. This single test resolves most scope arguments.
What almost always belongs
- The one core workflow, fully working end to end
- Basic authentication (even single-role)
- Enough data persistence to make the core workflow real, not simulated
What almost always waits
- Billing/subscription infrastructure
- Multiple user roles and admin tooling
- Edge-case handling for rare scenarios
- Polished, fully-branded UI (functional and clear is enough for validation)
Prototype, proof of concept or MVP
These three answer different questions. A prototype answers whether people understand the idea and would use it, and shows how it looks. A proof of concept answers whether something technical can be done at all, such as connecting to a system or handling a type of data. An MVP answers whether the product delivers value to real users in real use, with the smallest set of features that does.
Decide which question you actually have. If you already know the idea is wanted and the technology is proven, skip the first two and go to the MVP. See SaaS MVP development, and SaaS MVP vs internal tool if you are unsure whether the product is for customers or for your own team.
Why this discipline matters
Every feature added before validation is a bet made without user data. See How Much Does a SaaS MVP Cost for how directly this scope discipline affects price.
Questions
What if I already know I'll need billing eventually?+
Knowing you'll need it eventually is different from needing it in version one — it can be planned for architecturally without building it yet.
Isn't a narrow MVP a worse first impression?+
For real validation with real users, a working narrow product beats a broad, half-finished one — see What Happens When an AI Automation Fails for the general principle that a working narrow scope beats a broad fragile one.
Who decides what's 'core'?+
Whatever the single most important user action is — decided jointly during scoping, not assumed from a generic template.