# Thin Plan

> Convert a mini-spec into 3-7 vertical implementation slices.

- Skill: `tmusser/thin-plan` (Agent Skill)
- Install (CLI): `npx skillmds@latest add tmusser/thin-plan`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tmusser/thin-plan/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: tmusser (https://skillmd.com/u/tmusser)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tmusser/thin-plan

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# Thin Plan

## Purpose

Convert the mini-spec into 3-7 vertical implementation slices.

## When to use

Use when `SPEC.md` exists and implementation needs a short, ordered path.

## Inputs

- `SPEC.md`
- `CONTEXT.md`
- Existing repo structure
- Available verification commands

## Workflow

1. If `SPEC.md` has an active Contract ID, copy that ID exactly into `PLAN.md`. Do not invent an ID when SPEC has none.
2. Identify the smallest end-to-end behavior.
3. Create 3-7 slices that each produce observable behavior.
4. Make every slice independently verifiable.
5. Keep each slice to the fewest files possible.
6. Avoid horizontal architecture-only tasks unless required.
7. Record dependencies, risks, and verification strategy.
8. Write `PLAN.md` and `TODO.md`.

## Outputs

- `PLAN.md`
- `TODO.md`
- Active Contract ID in `PLAN.md` only when SPEC opted into contract identity

## Stop conditions

- Each task has a visible result and a check.
- Planning reveals a missing spec decision.

## Anti-patterns

- Planning all backend, then all frontend, then all tests.
- Creating broad tasks that cannot be finished in one session.
- Treating setup work as progress when no behavior changes.
- Inventing contract identity for work whose SPEC did not opt in.