# Arc42 Framework > Generate arc42 architecture documentation from a codebase. Read the repository into a structured evidence base, then author the 12 arc42 sections — emitting Mermaid diagrams where the code gives high-confidence structure, and explicit typed GAP flags where human input is needed, never fabricating. Use when asked to create, scaffold, or update arc42 docs, an architecture document, or per-section architecture views (building block view, runtime view, deployment view, etc.) for a project. - Skill: `florianbuetow/arc42-framework` (Agent Skill, multi-file: 21 files) - Install (CLI): `npx skillmds@latest add florianbuetow/arc42-framework` - Raw SKILL.md: https://api.skillmd.com/api/skills/florianbuetow/arc42-framework/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Docs & Writing - Author: florianbuetow (https://skillmd.com/u/florianbuetow) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/florianbuetow/arc42-framework --- Origin: plugin-original # arc42-framework This skill is the knowledge base behind the arc42 plugin. It turns a target codebase into arc42 architecture documentation by (1) reading the repo into a fact base and (2) authoring the twelve arc42 sections from that evidence. It does **not** copy arc42's prose; it routes each generated claim to recorded evidence, an explicit inference, or a typed GAP flag. The bundled references under `references/` are the plugin's working knowledge; the generated output format is fixed by `references/output-conventions.md`. --- ## Recipe overview 1. **Build the evidence base.** Parse manifests, import/dependency graphs, configs, IaC, route tables, and naming conventions into fact records (`F-NNN`) with a precise `source` and an `extraction_method`. This is the only place facts enter the system. 2. **Author sections in dependency order** (see Waves). Each sub-section pulls from the fact base, cites fact ids per claim, and chooses a diagram per `references/diagram-conventions.md`. 3. **Flag, never fabricate.** Where the code cannot answer, emit `GAP:human-input`; where evidence should exist but was not found, emit `GAP:no-evidence`. All gaps aggregate into `_gaps.md`. 4. **Lint and check consistency.** Apply `references/lint-checklist.md` (per-section rules) and `references/consistency-rules.md` (cross-section invariants) before delivery. The exact output layout, YAML front-matter, fact-record schema, per-sub-section `arc42-meta` blocks, per-claim anchors, and typed GAP flags are specified in `references/output-conventions.md`. --- ## Evidence-tier table Each section is classed by how far the code alone can carry it. The tier sets the default provenance and confidence, and decides whether a missing answer becomes a Mermaid diagram, a caveated diagram, or a `GAP:human-input`. | Tier | Meaning | Default output when evidence is thin | Sections | |------|---------|--------------------------------------|----------| | **code-derivable** | Structure is read directly from manifests, import graphs, configs, or route tables (high confidence) | Emit Mermaid directly; `GAP:no-evidence` only if the artifact is genuinely absent | §3 Context, §5 Building Block, §6 Runtime, §7 Deployment, §8 Crosscutting, §12 Glossary | | **code-inferable** | Reasoned from conventions, naming, or framework patterns (medium confidence) | Emit with an inline "derived from conventions — confirm" caveat | §2 Constraints, §4 Solution Strategy, §9 Architecture Decisions | | **human-input** | Business, quality, or intent decisions the code cannot reveal | Emit `GAP:human-input` with a specific question | §1 Introduction & Goals, §10 Quality, §11 Risks & Technical Debt | These tiers are recorded per section in `references/sections/NN-*.md` under `## Evidence tier`. --- ## Generation waves (code-derivable first) Sections are generated in three waves by the `generate` command. The wave order is **code-derivable structural sections first → dependent sections → synthesis**, not a strict topological sort of the `Depends on` edges declared in `references/sections/NN-*.md`. Cross-section consistency is enforced **post-hoc** by the consistency-checker (Phase C) — particularly the §3↔§5 interface symmetry (`interfaces-match`). Other `Depends on` edges are **best-effort cross-references**: a section may be authored before all of its declared upstream sections exist, and that is expected. Do not assume that all inputs pre-exist when a section is dispatched. - **Wave 0 — Evidence base.** Extract fact records from the repo. Precedes all sections. - **Wave 1 — §3 Context and Scope, §5 Building Block View, §7 Deployment View, §12 Glossary.** These four sections are code-derivable (structure readable directly from manifests, import graphs, IaC, and route tables). They run first with no prior wave output, in parallel. - **Wave 2 — §6 Runtime View, §8 Crosscutting Concepts, §4 Solution Strategy, §9 Architecture Decisions, §2 Constraints.** These five sections receive Wave 1 output as upstream context where available. Because §1 is not yet generated, upstream deps that reference §1 are absent and treated as best-effort. All five run in parallel. - **Wave 3 — §1 Introduction and Goals, §10 Quality, §11 Risks and Technical Debt.** These synthesis sections are authored last, after the structural and dependent sections are complete. §10 and §11 receive Wave 2 output. All three run in parallel. --- ## Why the knowledge base is *derived*, not copied The `references/` corpus is rewritten from the arc42 material rather than bundled verbatim, for four reasons: - **Licensing.** arc42 material is CC BY-SA 4.0. Derived, reworded, attributed references keep the plugin's obligations clean and auditable instead of shipping large verbatim excerpts. - **Portability.** The plugin ships self-contained reference files with no runtime dependency on the upstream arc42 site or its asset tree; generation works fully offline. - **Fitness for agents.** The corpus is restructured into machine-actionable artifacts — a lint checklist, cross-section consistency rules, a keyword taxonomy, a diagram-convention map, and an expected-topics catalog — which an agent can apply directly, unlike narrative documentation. - **Augmentation.** Each section spec adds plugin-original evidence-routing (what to look for in a repo, which extraction method, which Mermaid type, which GAP to emit) that arc42 itself does not provide, because arc42 documents the *template*, not how to derive it from code. ### Corpus Derivation Contract (the bar for future editors) Every arc42-derived reference file MUST keep sourcing from the crawled corpus snapshot (`.../crawl-arc42-doc/data/output`), MUST carry a `Source:` line citing the corpus-relative paths it derives from, MUST be reworded (no verbatim runs from the source), and MUST be accounted for in `references/COVERAGE.md` (every corpus file maps to a destination or a justified `dropped:` reason). Plugin-original files (this `SKILL.md`, `output-conventions.md`, `COVERAGE.md`) are marked `Origin: plugin-original` and need no `Source:`. The gate is `plugins/arc42/tests/check_corpus_contract.py`; keep it green and keep its `--corpus` pointed at the corpus root. --- arc42 is the work of Dr. Gernot Starke and Dr. Peter Hruschka; this knowledge base is derived from the arc42 framework material, used under CC BY-SA 4.0.