Build a SaaS With Claude in Vertical Slices
What it is
Building a SaaS with Claude by shipping thin vertical slices — one complete user story from database to UI — instead of building whole horizontal layers before anything runs.
Why it works
A finished data layer with no UI proves nothing and hides integration bugs until the end. A vertical slice is working software you can test and correct early, and it keeps Claude's work anchored to a real outcome rather than an abstract layer.
When to use it
Greenfield products and MVPs where you want momentum and early feedback. Best when you can name the single most important user story to build first.
When not to use it
Well-understood infrastructure work with no user-facing surface, where layer-by-layer can be clearer.
Prompt
We're building <product>. Let's work in vertical slices.
The first slice is this single user story: <story>. Take it end to end — data model, API, and minimal UI — the smallest version that actually works. List the slice's pieces first, then build them in order.Example
For a feedback-collection SaaS, the first slice is 'a user submits feedback and sees it saved' — model, endpoint, and a bare form — running and testable before any auth, dashboards, or styling exist.
Advanced version
Pair the slice approach with Claude Code so each slice is explored, planned, built, and tested in the real repo — and keep a running architecture note so later slices stay consistent.
Common mistakes
- Building the entire schema and API before a single screen exists, then discovering the flow is wrong.
- Making the first slice too fat, so 'minimal' quietly becomes the whole app.
- Not deploying early, so the first real integration surprise arrives at the worst time.