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.