Getting it into your agent
It runs from inside its repository, so the clone comes first — what it calls does not travel with the file alone.
git clone --depth 1 https://github.com/cynthiajones34/GBrainnpx agentmods add skills/cynthiajones34/gbrain/book-mirrorWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/cynthiajones34/gbrain/book-mirror)<a href="https://agentmods.dev/skills/cynthiajones34/gbrain/book-mirror"><img src="https://agentmods.dev/badge/skills/cynthiajones34/gbrain/book-mirror/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/cynthiajones34/gbrain/book-mirror"><img src="https://agentmods.dev/badge/skills/cynthiajones34/gbrain/book-mirror.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00072 | $0.03340 |
| Opus 5 | $0.00036 | $0.01670 |
| Sonnet 5 | $0.00014 | $0.00668 |
| Haiku 4.5 | $0.00007 | $0.00334 |
Grade A, and why
book-mirror scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
This is a copy
100% identical to book-mirror — 2 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.
How it starts
The opening of the file, as written. The whole thing — 351 lines — stays where its author put it; the contents beside it link to each section on GitHub.
book-mirror — Personalized Chapter-by-Chapter Book Analysis
Convention: see _brain-filing-rules.md for the sanctioned
media/<format>/<slug>exception this skill files under.Convention: see conventions/quality.md for citation rules, back-link enforcement, and output quality bars.
Convention: see conventions/brain-first.md for the lookup chain (brain → search → external) the context-gathering phase follows.
What this does
Given a book (EPUB or PDF), produce a brain page where every chapter is
summarized in detail on the left and mirrored back to the reader's actual life
on the right, using their own words, situations, people, and patterns from
the brain. Output is a brain page at media/books/<slug>-personalized.md.
This is NOT a generic book summary. The right column is the value: it makes the book read like a therapist who knows the reader is leaving notes in the margins. If the user wants a flat summary instead, route them to a different skill.
Trust contract (read this before running)
book-mirror runs as a CLI command (gbrain book-mirror), NOT as a pure
markdown skill that the agent dispatches via tools. The CLI is the trusted
runtime; the skill is the orchestration prose around it.
What this means for the agent:
- The CLI submits N read-only subagent jobs (one per chapter). Each subagent
has
allowed_tools: ['get_page', 'search']only. They CANNOT call put_page or any mutating op. They produce markdown analysis via their final message. - The CLI reads each child's
job.result, assembles the final two-column page, and writes it via a single operator-trustput_page. - This means untrusted EPUB/PDF content cannot prompt-inject any
people/*page. The trust narrowing happens at the tool allowlist, not at the slug-prefix layer.
The pipeline
1. ACQUIRE → User has the EPUB/PDF locally (manual; book-acquisition is
not currently shipped — see "Acquiring the book" below).
2. EXTRACT → Pull chapter text from EPUB/PDF into one .txt per chapter.
3. CONTEXT → Gather everything the brain knows about the reader.
4. ANALYZE → `gbrain book-mirror` fans out N read-only subagents.
5. ASSEMBLE → CLI reads each child result and writes one put_page.
6. PDF → Optional: render via skills/brain-pdf for delivery.
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 9d ago First seen · 351 lines · 72 tokens per session scan A e8b8cc7a6eba
book-mirror is a skill published in the GitHub repository cynthiajones34/GBrain (0 stars, last pushed 1mo ago), licensed MIT. It adds 72 tokens to every session and 3,340 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. It is 100% identical to book-mirror, differing in 2 lines, and is treated as a copy.
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