# Vertical Slice

> Build the smallest real end-to-end hackathon flow and test its riskiest dependency before expanding features or polishing the interface.

- Skill: `shreyp087/vertical-slice` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add shreyp087/vertical-slice`
- Raw SKILL.md: https://api.skillmd.com/api/skills/shreyp087/vertical-slice/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: Shreyp087 (https://skillmd.com/u/shreyp087)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/shreyp087/vertical-slice

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# Vertical slice

Create one usable path from representative input through the real mechanism to visible output. Start with existing code and the user's stack. For a blank project choose the smallest stack that meets the interaction, deployment, and team constraints.

Write a slice contract: actor, input, action, output, dependency, observable success, and failure behavior. Identify the assumption most likely to make the project impossible: data access, hardware capability, model quality, latency, or deployment support. Prove that assumption in a bounded spike first.

Define an interface with example payloads and error states before parallel implementation. Keep secrets server-side. Distinguish trusted application instructions from untrusted documents and model outputs at tool boundaries.

Implement a complete path with representative data. Fixtures are useful for independent UI work but label them and track when the real integration is required. Do not declare a feature working because a button returns a canned response.

Verify the slice with one meaningful happy path and the failure that threatens the demo most. Measure latency at the user boundary. Check the actual deployment target if its runtime differs from local development. Keep a reproducible input and a visible expected outcome.

Deliver code, exact run commands, evidence of execution, remaining limitation, and the smallest next extension. If the spike fails, give the observed cause and a workable scope reduction; do not bury it in a larger scaffold.