Rails Diff MCP Server

MCP server that exposes Rails version diffs as tools. Data comes from the railsdiff/rails-new-output GitHub repository, where each Rails version is tagged with the output of rails new.

Tools

Tool	Description
list_rails_versions	List all available Rails versions (sorted)
compare_rails_versions	Compare two versions — returns a list of changed files
get_file_diff	Get the patch for a specific file between two versions

Setup

Prerequisites

• Docker and Docker Compose
• Optional: GITHUB_TOKEN env var to avoid GitHub API rate limits

Start the server

docker compose up -d

The server listens on http://localhost:8080/mcp with a health check at http://localhost:8080/healthz.

Register in your MCP client

Example for Claude Code:

claude mcp add --transport http rails-diff http://localhost:8080/mcp

Restart your MCP client to pick up the new server.

Development

bun install
bun src/index.ts

The server starts on port 8080 by default. Override with PORT env var.

Configuration

Env var	Description	Default
PORT	Server listen port	8080
GITHUB_TOKEN	GitHub personal access token (raises API rate limit)	none

Credits

Built on top of RailsDiff by Andy Stewart and contributors. The diff data comes from railsdiff/rails-new-output.