# 0018 — factory/write-skill (bootstrap skill)

**Type:** HITL  
**Parent PRD:** `docs/prd/chunk-3-skills-library.md`

## What to build

Build `write-skill` — the second bootstrap skill, immediately after `write-eval`. Once `write-skill` exists, it is used to author all subsequent SKILL.md files in Chunk 3 rather than writing them by hand.

**Trigger description** (from skills index): "Write a new skill for X, create a SKILL.md that does Y"

**Key constraints:**
- Produces a complete SKILL.md following the authoring standard (frontmatter, role, when/when-not, required inputs, constraints, process, output format, failure handling)
- Validates trigger description against three test queries (explicit, implicit, negative) before completing
- Flags if the proposed skill overlaps with an existing skill in the library
- Skill file: `.agents/skills/write-skill/SKILL.md`; `metadata.category: factory`
- Origin: new skill (check upstream for prior art during implementation); `source:` populated only if upstream content is adopted
- Eval via `write-eval` (issue 0017)

Process: upstream review → trigger-first → skill body → `write-eval` for eval.yaml → behavioral test.

## Implementation notes

Follow the per-skill workflow defined in `docs/notes/skill-implementation-workflow.md` (produced by issue 0016).

**Known upstream sources to review:**
- `mattpocock/skills` — contains `write-a-skill`, the direct Pocock equivalent; review at current HEAD; record SHA in `source:` for any adopted content
- agentskills.io open standard — the SKILL.md format spec is the authoritative reference for what `write-skill` must produce; cross-reference against the standard before finalising output format constraints
- `bmad-method/bmad-method` — check for any skill-authoring or template-writing patterns

## Acceptance criteria

- [ ] `.agents/skills/write-skill/SKILL.md` exists; `metadata.category: factory`; authoring standard met
- [ ] Trigger description validates against explicit, implicit, and negative test queries
- [ ] `.agents/evals/factory/write-skill/eval.yaml` exists; produced via `write-eval`
- [ ] `install.sh` deploys `write-skill` to `~/.agents/skills/`
- [ ] **HITL:** human runs behavioral test: invoke "write a new skill for X" and verify the produced SKILL.md meets the authoring standard
- [ ] **HITL:** human reviews SKILL.md and eval before committing
- [ ] _(Further criteria to be refined after issue 0016 grill session)_

## Blocked by

- 0016 (grill defines per-skill workflow)
- 0017 (`write-eval` needed to produce the eval for this skill)