# C3

> Use when project needs C3 adoption (no .c3/) or auditing existing C3 docs. Triggers: "adopt C3", "onboard", "scaffold", "audit", "validate", "check C3", "init". NOT for navigation (use c3-query) or changes (use c3-alter).

- Skill: `majiayu000/c3` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds add majiayu000/c3`
- Raw SKILL.md: https://api.skillmd.com/api/skills/majiayu000/c3/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Security
- Author: majiayu000 (https://skillmd.com/u/majiayu000)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/majiayu000/c3

---


# C3 Architecture Assistant

## Skill Routing

| Intent | Skill |
|--------|-------|
| "Where is X?" / Explore | `c3-query` |
| "Add/change X" | `c3-alter` |
| "Audit C3" | This skill |
| No `.c3/` exists | This skill (Adopt) |

## REQUIRED: Check Activation

**Before proceeding, check if `.c3/README.md` exists.**

- If NO `.c3/`: This is **Mode: Adopt**. Suggest `/onboard` or proceed with adoption.
- If YES `.c3/`: Route based on intent (Audit stays here, others route to dedicated skills).

## ADR Lifecycle

`proposed` → `accepted` → `implemented`

See `references/adr-template.md` for template.

## Mode: Adopt

**Template-first approach.** Two rounds:

### Round 1: Structure (User runs bash)

```bash
PROJECT="MyApp" C1="backend" C2="frontend" ./scripts/c3-init.sh
```

Creates:
```
.c3/
├── README.md                       (Context)
├── c3-1-backend/README.md          (Container)
├── c3-2-frontend/README.md         (Container)
└── adr/adr-00000000-c3-adoption.md (ADR)
```

### Round 2: Fill (AI subagent)

Dispatch subagent to analyze codebase and fill templates:

**Context (c3-0):**
1. Analyze codebase for actors (users, schedulers, webhooks)
2. Confirm containers match code structure
3. Identify external systems (databases, APIs, caches)
4. Draw mermaid diagram with IDs (A1, c3-1, E1, etc.)
5. Fill linkages with REASONING (why they connect)

**Each Container (c3-N):**
1. Analyze container scope for components
2. Categorize by concern:
   - Foundation: entry, identity, integration
   - Auxiliary: library wrappers, framework usage, utilities
   - Business: domain services
   - Presentation: styling, composition, state (or N/A)
3. Draw internal mermaid diagram with component IDs
4. Fill fulfillment section (which components handle Context links)
5. Fill linkages with REASONING

**ADR-000:**
1. Document why C3 was adopted
2. List all containers created
3. Mark verification checklist

**Reference:** See `references/container-patterns.md` for component categorization patterns.

### Subagent Prompt Template

```
You are filling C3 templates for {{PROJECT}}.

Templates are already in place at .c3/. Your job:
1. Analyze codebase
2. Fill inventory tables
3. Create mermaid diagrams with IDs
4. Add linkages with reasoning

Rules:
- Diagram goes FIRST, uses IDs from tables
- Every linkage needs REASONING (why, not just that)
- Foundation/Auxiliary/Business/Presentation categories
- Fulfillment section maps Context links to components
- Keep structure, fill content
```

## Mode: Design

**Defer to `c3-alter` skill** for all architecture and code changes.

`c3-alter` enforces ADR-first workflow with impact discovery.

## Mode: Audit

**REQUIRED:** Load `references/audit-checks.md` for comprehensive audit procedures.

Quick reference scopes:
- `audit C3` - full system
- `audit container c3-1` - single container
- `audit adr adr-YYYYMMDD-slug` - single ADR

The reference contains detailed checks for:
- Diagram-inventory consistency
- ID uniqueness
- Linkage reasoning
- Fulfillment coverage
- Orphan detection

## Guidelines

- Diagram first, tables second, linkages third
- Every linkage needs reasoning
- Container fulfills Context links (documents constraints)
- Component documents implementation (technology, conventions, edge cases)
- Inventory ready for growth (empty sections OK)