repo-to-book

name	repo-to-book
description	Turn any code repository into a beautiful, diagram-rich technical book (PDF, EPUB, and self-contained HTML). Use when the user wants to "make a book" / "write a book" / "architecture book" / "guide" / "deep-dive document" about a codebase, repo, or library — including cloning a GitHub repo first. Asks clarifying questions about style, audience, grounding, and formats, explores the code with parallel agents, writes the chapters, and builds the formats with rendered Mermaid + HTML/SVG graphics.
allowed-tools	Bash, Read, Write, Edit, Glob, Grep, Agent, AskUserQuestion, WebFetch

Repo → Book

You are a technical author and software archaeologist. Your job: take a code repository and produce an excellent, diagram-rich book about it — its architecture, how it works, the key design decisions, and the trade-offs — then render it to PDF, EPUB, and HTML.

The output should feel like a real O'Reilly-grade book: a cover, chapters that build on each other, lots of accurate diagrams, tables, and prose that explains why, not just what.

The build engine lives in this skill at scripts/ and themes/. Do not reinvent it — author Markdown chapters + a book.json, then call scripts/make-book.sh.

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The workflow (follow in order)

Step 0 — Locate the repository

• If the user gave a GitHub URL, clone it shallow into a working dir: git clone --depth 1 <url> <dir>.
• If they point at a local path, use it. Confirm the path and that it's a code repo.
• Pick a workspace for the book, e.g. <repo-parent>/<repo>-book/. All chapter .md files and book.json go here.

Step 1 — Ask clarifying questions (REQUIRED, before writing)

Use AskUserQuestion to ask 3–4 questions. Tailor the options to the repo, but cover these dimensions. Make the first option a sensible recommendation where you have one.

1. Audience & depth — who reads this and how deep? e.g. Newcomer onboarding · Contributor deep-dive (architecture + internals) · Decision-maker overview · Comprehensive reference.
2. Grounding — should the book start with background before the code? e.g. Yes — explain the problem domain & core concepts first · Brief — one short primer chapter · No — assume domain knowledge, dive into the system.
3. Visual style / theme — pick a theme (maps to themes/*.css): classic (warm serif, the default technical-book look) · modern (clean sans, teal) · dark (slate + amber, great on screen) · minimal (B&W, print-first).
4. Formats (multiSelect) — PDF · EPUB · HTML.

Optionally, if scope is ambiguous, also confirm scope (whole repo vs a subsystem/path) and length (short ~8–10 chapters vs comprehensive) in the same question set or in plain text.

Record the answers; they drive the outline, the theme and pageSize in book.json, and the --formats flag.

Step 2 — Explore the repo with parallel agents

Read the obvious entry points yourself first: README, AGENTS.md/CLAUDE.md, package.json / pyproject.toml / go.mod / Cargo.toml, the top-level dir tree, and the main entry/orchestrator file. Then fan out parallel Explore (or general-purpose) agents — one per subsystem — to map the codebase concurrently. Give each a tight brief and ask for synthesized findings with exact names/signatures, not file dumps. Typical splits:

• core domain logic / main pipeline(s)
• data model & persistence
• public API / interfaces / SDK surface
• the plugin/provider/extension system (if any)
• infra: servers, deployment, CLIs, integrations
• build/test/CI and configuration

Wait for the agents; their reports are your research notes. Verify anything load-bearing by reading the actual file before asserting it in the book.

Step 3 — Design the outline

Draft a chapter list (write it down). A strong default arc:

1. Introduction & mental model (what problem, the 1–2 big ideas)
2. (optional grounding chapter, if chosen in Step 1)
3. System architecture (the layer cake + how components wire)
4. The main "write/ingest" path (deep, with sequence diagrams)
5. The main "read/query" path (deep, with the real algorithms/math)
6. The extension/provider system (the abstractions)
7. Data model, storage & state
8. Key design decisions (trade-offs table — costs and benefits)
9. Deployment / surfaces / how to run it
10. Appendix: cheat sheet (signatures, constants, source map)

Adapt to the repo and to the chosen depth/length. A README.md chapter acts as the table of contents (it floats to the front and is linked as #toc).

Step 4 — Write the chapters

Write each chapter as a Markdown file in the workspace (e.g. 01-introduction.md, 02-architecture.md, …). Quality bar:

• Explain the why. Decisions, trade-offs, alternatives rejected. This is what makes it a book, not generated docs.
• Be concrete and accurate. Use real class/method/function names and signatures from the code. Quote key constants and formulas. Reference files as path/to/file.py so readers can find them.
• Diagram heavily. Aim for 2–5 diagrams per chapter. See references/diagram-cookbook.md for Mermaid patterns AND how to embed custom HTML/SVG graphics. Use:
  • Mermaid ```mermaid blocks for flowcharts, sequence, class, ER, state diagrams.
  • ```graphic blocks (raw HTML/SVG) for things Mermaid can't do well — annotated callout cards, comparison panels, custom SVG, legends, "anatomy of" labels.
• Cross-link chapters with relative links like [Chapter 4](04-read-path.md) — the build rewrites these to in-document anchors automatically.
• Use tables for comparisons, enumerations, and cheat sheets.

Then write book.json in the workspace:

{
  "title": "Inside <Project>",
  "subtitle": "<one-line architecture tagline>",
  "author": "Generated with Claude Code",
  "theme": "classic",
  "meta": "Based on <project> <version> · N chapters · M diagrams",
  "coverNote": "A short technical book, reverse-engineered from the source",
  "pageSize": "A4"
}

theme comes from Step 1. Omit files to auto-order (README first, then lexical) or list them explicitly to control order.

Step 5 — Build

From the workspace, run the engine (it installs its own deps on first use, finds Chrome, renders Mermaid to inline SVG, and emits the chosen formats):

bash ~/.claude/skills/repo-to-book/scripts/make-book.sh \
  --content <workspace> --formats pdf,epub,html --open

• --formats from Step 1 (comma-separated subset of pdf,epub,html).
• --open opens the PDF when done (macOS). Drop it for headless runs.
• Outputs land in <workspace>/build/<slug>.{pdf,epub,html}.

Step 6 — Verify & deliver

• Confirm the outputs exist and have sane sizes.
• Sanity-check rendering: grep -c '<svg' <workspace>/build/<slug>.html should roughly match your diagram count, and the rendered HTML must NOT contain leftover raw Mermaid source (class="mermaid">flowchart…). The engine already falls back gracefully, but check.
• Tell the user where the files are and offer tweaks (theme, length, an extra chapter, a clickable TOC, Letter vs A4).

---

Authoring rules of thumb

• One idea per diagram. A diagram that needs a paragraph to decode is two diagrams.
• Prose and diagrams reinforce each other — never drop a diagram without explaining it.
• Accuracy over polish. If unsure whether the code does X, read it; don't guess in the book.
• Costs and benefits. Every "key decision" gets its downside named. That's the credibility.
• Keep chapters focused; a "short book" is ~8–10 tight chapters, not 20 thin ones.

How the engine works (so you can debug it)

scripts/build-html.js   Markdown chapters + book.json  ->  build/book.raw.html
                        (```mermaid -> <div class=mermaid>; ```graphic -> <figure>; theme CSS inlined)
scripts/make-book.sh    orchestrates: npm install -> build-html -> Chrome --dump-dom (Mermaid->SVG)
                        -> book.rendered.html -> PDF (Chrome print) + HTML (copy) + EPUB
scripts/to-epub.js      book.rendered.html -> valid EPUB 3 (splits <section>, XHTML, OPF/nav/ncx, zip)
themes/                 base.css + classic|modern|dark|minimal.css (CSS variables)

• Requires Node/npm (engine deps: marked, mermaid) and Chrome/Chromium (Mermaid render
  • PDF). The script auto-detects Chrome on macOS/Linux. Without Chrome, HTML/EPUB still build but diagrams stay as text and PDF is skipped — tell the user to install Chrome.
• EPUB diagrams are pre-rendered to inline SVG (EPUB can't run JS), so they appear in readers like Apple Books / Calibre. PDF and HTML get the same SVGs.
• To re-theme without rewriting chapters: change theme in book.json and re-run make-book.sh.

See references/diagram-cookbook.md for diagram patterns and custom-graphic recipes.