The first thin slice
Why we ship something real, end to end, to real users within the first weeks — and what it has to include.
A thin slice is one narrow path through the whole system: one type of request, one user, one outcome — running in production infrastructure with monitoring and a deployment pipeline behind it.
What it proves
That the architecture holds. That the integrations actually work with the real systems, not the documentation. That users understand it. Every one of these is cheaper to discover in week three than in month nine.
What it must include
Authentication, logging, deployment, a test suite and a rollback path. Skipping these makes the slice a prototype, and prototypes have a way of becoming production without anyone deciding.
What it must not include
Every edge case. Configuration screens. The reporting module. Breadth comes later; the slice is about depth.