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mcp-on-rails: Instructions file for Claude Code

CLAUDE.md

mcp-on-rails CLAUDE.md is an instructions file for Claude Code from pstrzalk/mcp-on-rails. It costs 1,930 tokens per session, scanned A, original, MIT.

Repository instructions for an MCP on Rails project. MCP is a standard way for applications to expose tools that an AI agent can call.

In plain words
What is it for?
Creating Rails applications with MCP support, configuring open or OAuth-protected access, and maintaining the template and its generated code.
Why use it?
They explain how the Rails template, generated tools, server endpoint, and optional login system fit together.

Instructions file for Claude Code

Written for Claude Code: the file is CLAUDE.md. Also seen: mentions CLAUDE.md; mentions Claude Code.

This is pstrzalk/mcp-on-rails's own configuration. It tells Claude Code how to work on mcp-on-rails itself, so it is not a mod to install elsewhere. Copy it as a starting point and replace the rules that are about this project. Everything mcp-on-rails configures →

not rated 150repo 7mo ago A scan 1,930 tokens original MIT
View source ↗ pstrzalk/mcp-on-rails
Reuse

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.

Copy the file
curl -O https://raw.githubusercontent.com/pstrzalk/mcp-on-rails/main/CLAUDE.md
Clone the repo
git clone --depth 1 https://github.com/pstrzalk/mcp-on-rails

Made for: Claude Code.

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Per session 1,930 This file is loaded in full into every session.
When invoked 1,930 The same file — it is already loaded in full.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
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 $0.01930 $0.01930
Opus 5.5 $0.00772 $0.00772
Sonnet 5.5 $0.00386 $0.00386
Haiku 4.5 $0.00193 $0.00193

Measured 2mo ago against content hash 1214abe851d9, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

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 2mo 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.

CLAUDE.md · 177 lines

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:

  1. mcp - The Rails application template file
  2. mcp_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:

  1. Adds the mcp gem (and optionally devise + doorkeeper) to the Gemfile
  2. Copies template files from mcp_template/ directory
  3. Creates an McpController that handles MCP protocol requests at /mcp endpoint (streamable HTTP transport)
  4. Sets up Rails generator hooks for automatic MCP tool generation during scaffolding
  5. Adds a to_mcp_response method to ActiveRecord models for consistent MCP formatting
  6. Configures Rails to ignore generators from autoloading
  7. 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.

Read the full file on GitHub · 177 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. 2mo ago First seen · 177 lines · 1,930 tokens per session scan A 1214abe851d9

Subscribe to this mod's changes

mcp-on-rails CLAUDE.md is an instructions file published in the GitHub repository pstrzalk/mcp-on-rails (150 stars, last pushed 7mo ago), licensed MIT. It adds 1,930 tokens to every session, about $0.0077 per session on Opus 5.5. 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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