---
name: milestone-planning
description: Guide for planning development milestones and generating milestone documents with a feature breakdown. Use when planning milestones, a release roadmap, or deciding implementation order under docs/milestones/.
allowed-tools: Read, Write, Edit
---

# Milestone Planning Skill

This skill explains how to break a product into ordered milestones and produce milestone documents under `docs/milestones/`. The documents are the bridge between the specification (`docs/`) and implementation (`/add-feature`): every feature in every milestone is sized to be implemented with **one `/add-feature` run**.

## Core Principles

1. **MVP first**: Milestone 1 is the smallest coherent, end-to-end usable product. Not a layer (e.g. "all the models"), but a vertical slice a user could actually use.
2. **Vertical slices**: Each feature cuts through UI → logic → data. Avoid horizontal milestones like "backend milestone" / "frontend milestone".
3. **One feature = one `/add-feature` run**: If a feature needs more than one steering directory to implement, split it. If it is a one-line change, merge it into a neighbor.
4. **Dependency order**: A feature never lands in an earlier milestone than something it depends on.
5. **Exactly-once assignment**: Every feature belongs to exactly one milestone. Deliberately deferred items go to the roadmap's "Later / Icebox" — nothing silently disappears.
6. **Living documents**: Milestone documents track status. `/add-feature` checks off a feature (`[ ]` → `[x]`) when it completes, and the roadmap status is updated when a milestone finishes.

## Inputs

Before planning, read:

- `docs/product-requirements.md` — user stories, priorities (P0/P1/P2), success metrics
- `docs/functional-design.md` — functional modules and data flows
- `docs/architecture.md` — technical constraints and dependencies
- `docs/design/ui-blueprint.json` (if present) — screens and user actions
- `docs/ideas/*` (if present)

## Outputs

```
docs/milestones/
├── roadmap.md                      # Overview: milestone table, ordering rationale, icebox
├── milestone-01-[name].md          # MVP
├── milestone-02-[name].md
└── milestone-NN-[name].md
```

File naming: `milestone-[NN]-[kebab-case-name].md` (e.g. `milestone-01-mvp.md`, `milestone-02-collaboration.md`).

Use the structure in `template.md` for each milestone document.

## How to Slice Features

A well-sized feature:

- Delivers observable user value (or unblocks one that does)
- Touches one primary screen/flow (may touch shared components)
- Has 3–7 acceptance criteria
- Can be described in one sentence starting with a verb ("Edit user profile", "Filter tasks by tag")
- Works verbatim as a command argument: `/add-feature Edit user profile`

Too big (split it): "User management" → "Register account", "Log in / log out", "Edit user profile", "Reset password".
Too small (merge it): "Change button color" → fold into the feature that owns that screen.

## How to Group Milestones

1. Tag every feature with its PRD priority and its dependencies.
2. Milestone 1 (MVP): the minimal dependency-closed set of P0 features that forms a usable product walk-through (a user can start, do the core job, and finish).
3. Following milestones: group remaining features by theme and priority, keeping each milestone a meaningful release on its own ("after milestone N ships, the user can additionally …").
4. Prefer 2–4 milestones with 3–8 features each. More than ~8 features in one milestone usually means it should be split.

## Status Tracking Rules

- Feature status lives **only** in the feature checkbox of its milestone document.
- Milestone status (`Not started` / `In progress` / `Completed`) lives in both the milestone document header and the roadmap table — keep them in sync.
- `/add-feature` Step 8 updates the feature checkbox and, when the last feature of a milestone completes, the milestone and roadmap statuses.
- Re-planning (adding/moving/removing features) must update both the milestone document(s) and `roadmap.md` in the same change.

## Consistency Checklist

Before finishing:

- [ ] Every P0/P1 PRD requirement maps to a feature in some milestone (or is explicitly in the icebox).
- [ ] Every feature appears in exactly one milestone.
- [ ] No feature precedes one of its dependencies.
- [ ] Milestone 1 is a usable end-to-end product on its own.
- [ ] Every feature has acceptance criteria and a ready-to-run `/add-feature` command line.
- [ ] `roadmap.md` table matches the milestone documents (names, counts, statuses).