libretto-readonly

libretto-readonly is a skill for Claude Code from saffron-health/libretto. It costs 26 tokens per session (1,009 once invoked), scanned A, original, MIT.

A read-only Libretto workflow for inspecting the current state of a live browser session. It allows observation without clicking, typing, navigating, submitting forms, or changing application data.

In plain words
What is it for?
Use it to inspect page titles, HTML, visible text, element counts, visibility, and results from safe GET requests.
Why use it?
It lets an agent diagnose what a browser currently shows while reducing the risk of accidental changes. Libretto is the browser-inspection system described by this skill.

Skill for Claude Code

Written for Claude Code: shipped in a Claude Code plugin. Also seen: installed under .agents/ (shared by several agents).

Part of the libretto plugin — 24 skills shipped together

Good fit Use it to inspect page titles, HTML, visible text, element counts, visibility, and results from safe GET requests.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/saffron-health/libretto/libretto-readonly
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add saffron-health/libretto --skill libretto-readonly
Clone the repo
git clone --depth 1 https://github.com/saffron-health/libretto

Made for: Claude Code.

Or install libretto, the plugin that ships this one along with the rest of its 24 skills.

Wrote 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.

agentmods badge for libretto-readonly

README.md
[![agentmods](https://agentmods.dev/badge/skills/saffron-health/libretto/libretto-readonly/github.svg)](https://agentmods.dev/skills/saffron-health/libretto/libretto-readonly)
Your own site
<a href="https://agentmods.dev/skills/saffron-health/libretto/libretto-readonly"><img src="https://agentmods.dev/badge/skills/saffron-health/libretto/libretto-readonly/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.

agentmods 80×15 button for libretto-readonly

Your own site · 80×15
<a href="https://agentmods.dev/skills/saffron-health/libretto/libretto-readonly"><img src="https://agentmods.dev/badge/skills/saffron-health/libretto/libretto-readonly.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 26 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,009 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 1 finding, up to medium

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • medium Data Exfiltration · line 77
    Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.
    Fix: Verify the destination URL is trusted and necessary. Remove or replace with documented APIs. Ensure no secrets, tokens, or PII are transmitted.
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00026 $0.01009
Opus 5 $0.00013 $0.00504
Sonnet 5 $0.00005 $0.00202
Haiku 4.5 $0.00003 $0.00101

Measured 10d ago against content hash ff41091a7efb, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

libretto-readonly 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 10d 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.

.agents/skills/libretto-readonly/SKILL.md · 91 lines

How it starts

The opening of the file, as written. The whole thing — 91 lines — stays where its author put it; the contents beside it link to each section on GitHub.

How Libretto Read-Only Works

  • Use this skill when the browser session must stay strictly read-only.
  • Libretto stores read-only vs write-access on the session itself.
  • The primary inspection tools are snapshot and readonly-exec.
  • readonly-exec reuses Libretto's normal execution pipeline, but it only exposes read-only helpers and denies mutating Playwright methods.
  • Only a user can change the session mode for an existing session. Never change a session's mode on your own — the user must change it themselves manually.

Working Rules

  • Announce which session you are using and what page you are inspecting.
  • Do not use exec, run, or any direct Playwright action that could change browser or application state.
  • Do not click, type, submit forms, navigate, upload files, dispatch DOM events, or send non-GET requests.
  • Prefer snapshot first when the visible page state is unclear.
  • Use readonly-exec for focused inspection: titles, HTML, locator text, counts, visibility checks, and GET requests.
  • Keep snippets small and purpose-built. Do not run multiple readonly-exec commands at the same time.
  • Close disposable sessions before your final response once inspection is complete. Open browsers keep consuming local or hosted resources.
  • End with diagnosis and handoff guidance, not an attempted in-browser repair.

Commands

connect

  • Use connect to attach to an existing CDP endpoint for a preserved browser session.
  • Use --read-only when creating the Libretto session handle for a preserved browser session.
  • Libretto read-only mode is enforced through Libretto commands; direct CDP clients that skip Libretto are outside this boundary.
libretto connect http://127.0.0.1:9222 --read-only --session failed-job-debug

pages

  • Use pages when a popup, new tab, or second page exists.
  • If readonly-exec or snapshot complains about multiple pages, list ids first and then pass --page.
libretto pages --session failed-job-debug

Read the full file on GitHub · 91 lines

Changes

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.

  1. 10d ago First seen · 91 lines · 26 tokens per session scan A ff41091a7efb

Subscribe to this mod's changes

libretto-readonly is a skill published in the GitHub repository saffron-health/libretto (889 stars, last pushed 19d ago), licensed MIT. It adds 26 tokens to every session and 1,009 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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