Borrowing it
Nothing to install: this file belongs to pstrzalk/mcp-on-rails. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/pstrzalk/mcp-on-rails/main/CLAUDE.mdgit clone --depth 1 https://github.com/pstrzalk/mcp-on-railsWrote 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/instructions/pstrzalk/mcp-on-rails/claude-md)<a href="https://agentmods.dev/instructions/pstrzalk/mcp-on-rails/claude-md"><img src="https://agentmods.dev/badge/instructions/pstrzalk/mcp-on-rails/claude-md.svg" alt="Measured on agentmods" 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 | $0.01930 | $0.01930 |
| Opus 5 | $0.00965 | $0.00965 |
| Sonnet 5 | $0.00386 | $0.00386 |
| Haiku 4.5 | $0.00193 | $0.00193 |
Grade A, and why
mcp-on-rails CLAUDE.md 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 8d 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.
How it starts
The opening of the file, as written. The whole thing — 177 lines — stays where its author put it; the contents beside it link to each section on GitHub.
CLAUDE.md
This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
Project Description
This is an MCP on Rails template - a Rails application template that seamlessly integrates the Model Context Protocol (MCP) with Ruby on Rails applications using the mcp gem.
The template supports two modes — plain MCP (open endpoint) and OAuth MCP (Devise + Doorkeeper with OAuth 2.1, PKCE, dynamic client registration, and resource indicators). The mode is selected interactively during setup.
The project consists of two main components:
mcp- The Rails application template filemcp_template/- Directory containing template files copied to new Rails applications
The mcp template bootstraps a new Rails app with MCP server capabilities. When run with rails new myapp -m mcp, it:
- Adds the
mcpgem (and optionallydevise+doorkeeper) to the Gemfile - Copies template files from
mcp_template/directory - Creates an
McpControllerthat handles MCP protocol requests at/mcpendpoint (streamable HTTP transport) - Sets up Rails generator hooks for automatic MCP tool generation during scaffolding
- Adds a
to_mcp_responsemethod to ActiveRecord models for consistent MCP formatting - Configures Rails to ignore generators from autoloading
- Optionally sets up OAuth 2.1 with Devise authentication, Doorkeeper OAuth provider, PKCE enforcement, dynamic client registration (RFC 7591), authorization server metadata (RFC 8414), protected resource metadata (RFC 9728), and resource indicators (RFC 8707)
When you scaffold new models (rails generate scaffold Post title:string), MCP tools are automatically generated alongside standard Rails files (the generator prompts to select All, Some, or None), providing AI assistants with structured access to CRUD operations.
How Rails generators work:
Read contents of https://raw.githubusercontent.com/rails/rails/refs/heads/main/guides/source/generators.md to get context about Rails generators.
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.
- 8d ago First seen · 177 lines · 1,930 tokens per session scan A 1214abe851d9
mcp-on-rails CLAUDE.md is an instructions file published in the GitHub repository pstrzalk/mcp-on-rails (145 stars, last pushed 5mo ago), licensed MIT. It adds 1,930 tokens to every session, about $0.0097 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.
Other instructions, from other repositories
codex AGENTS.md
AGENTS.md instructions for openai/codex, covering rust/codex-rs, the codex-core crate, code review rules, crate api surface and model visible context.
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
next.js AGENTS.md
AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
langchain AGENTS.md
AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, applying the notice (cutover) and fallback chain (never fail the build).
spec-kit AGENTS.md
AGENTS.md instructions for github/spec-kit, covering agents.md, about spec kit and specify, quickstart — add a new integration in 5 steps, integration architecture and integrationmanifest — file tracking.