rtfmbro

rtfmbro is a cursor rule for Cursor from marckrenn/rtfmbro-mcp. It costs 417 tokens per session, scanned A, original, MIT.

A set of Cursor editor instructions requiring the coding agent to read official package documentation before using a library or module. It also describes how to find the exact version in a project's lock file, which records pinned dependencies.

In plain words
What is it for?
Checking dependency versions, fetching their documentation, and guiding package-related coding work when the agent is uncertain.
Why use it?
It reduces mistakes caused by outdated assumptions about a package's behavior, configuration, or available functions.

Cursor rule for Cursor

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.

agentmods
npx agentmods add rules/marckrenn/rtfmbro-mcp/rtfmbro
Clone the repo
git clone --depth 1 https://github.com/marckrenn/rtfmbro-mcp

Made for: Cursor.

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 rtfmbro

README.md
[![agentmods](https://agentmods.dev/badge/rules/marckrenn/rtfmbro-mcp/rtfmbro.svg)](https://agentmods.dev/rules/marckrenn/rtfmbro-mcp/rtfmbro)
Your own site
<a href="https://agentmods.dev/rules/marckrenn/rtfmbro-mcp/rtfmbro"><img src="https://agentmods.dev/badge/rules/marckrenn/rtfmbro-mcp/rtfmbro.svg" alt="Measured on agentmods" height="20"></a>
Per session 417 This file is loaded in full into every session.
When invoked 417 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
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 $0.00417 $0.00417
Opus 5 $0.00209 $0.00209
Sonnet 5 $0.00083 $0.00083
Haiku 4.5 $0.00042 $0.00042

Measured 4d ago against content hash 74ce4e51f2be, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

rtfmbro 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 4d 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.

.cursor/rules/rtfmbro.mdc · 32 lines

What it actually says

Cursor Instructions for Package Documentation

Package Documentation Policy

  • Before using any package, module, or library, ALWAYS consult its documentation — your internal knowledge may be outdated and could cause errors or failures.
  • Don't assume anything about the package's functionality, usage, or configuration without verifying it against the official documentation.
  • If you are unsure about a user's request that may involve a package, module, or library, ALWAYS refer to the documentation first or ask the user to provide the package name and version.

Workflow

  1. Don't immediately lookup the user's original codebase.
  2. First, Identify the package name and the EXACT pinned version (eg. "==1.0.5") from the project’s lock file (eg. uv.lock, bun.lock).
  3. Using this information fetch documentation by executing one of the provided tools:
    • get_readme
    • get_documentation_tree
    • read_files
    • search_github_repositories - Search for Github packages and repositories by topic, language, or keywords. Note, sometimes the documentation is located in a separate repository (like tailwindlabs/tailwindcss.com). Use the repo owner to search for the repo containing the documentation.
  4. Review the documentation carefully to understand:
    • Core functionality
    • Usage patterns
    • Any caveats or special instructions
  5. Reference examples from the documentation to guide your implementation.

Ecosystem Selection:

  • Use pypi for Python packages
  • Use npm for Node.js packages
  • Use spm for Swift packages
  • Use gh only as a fallback for languages not supported by the above registries (package name must be in 'owner/repo' format) or if you're unsure about the package's ecosystem. Also use gh when you don't find the package in the lock file.
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. 4d ago First seen · 32 lines · 417 tokens per session scan A 74ce4e51f2be

Subscribe to this mod's changes

rtfmbro is a cursor rule published in the GitHub repository marckrenn/rtfmbro-mcp (91 stars, last pushed 1y ago), licensed MIT. It adds 417 tokens to every session, about $0.0021 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.