ruby_event_store-mcp

Model Context Protocol (MCP) server for RubyEventStore. Exposes your event store as AI tools so Claude (and other MCP clients) can inspect streams, events, and causal relationships directly.

Installation

Add to your Rails app's Gemfile:

gem "ruby_event_store-mcp"

Usage

Run from the root of your Rails application:

bundle exec res-mcp

The server communicates over stdio using the MCP protocol. Installing the gem only provides the res-mcp binary — you still have to register it with your MCP client. Every client takes the same server definition; only the file it lives in differs.

Claude Code

Add a .mcp.json to your project root (or run claude mcp add res -- bundle exec res-mcp):

{
  "mcpServers": {
    "res": {
      "command": "bundle",
      "args": ["exec", "res-mcp"]
    }
  }
}

Launched from the project directory, Claude Code runs the server there, so no cwd is needed. On the next launch Claude Code asks you to trust the server — approve it, then run /mcp to confirm res is connected with its tools.

Claude Desktop

Add the same block with an explicit cwd pointing at your app's root, in claude_desktop_config.json:

{
  "mcpServers": {
    "res": {
      "command": "bundle",
      "args": ["exec", "res-mcp"],
      "cwd": "/path/to/your/rails/app"
    }
  }
}

Config file locations:

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

Other MCP clients

Cursor, Windsurf, Cline and others take the same mcpServers block in their own config file. VS Code's built-in MCP support uses a servers key with "type": "stdio" instead. The bundle exec res-mcp command is the portable part.

Requirements

• Ruby >= 3.0
• A Rails application with Rails.configuration.event_store configured

Available tools

Tool	Description
recent	Most recent events across all streams (default: 20, newest first)
stream_show	Event count, version, first/last event for a stream
stream_events	List events in a stream (filter by type, time range, limit)
event_show	Full event details: data, metadata, timestamps
event_streams	All streams an event has been published or linked to
aggregate_history	Full event history of an aggregate instance by type and ID
search	Search events by type, time range, or stream
stats	Total event count and unique event types
trace	Causation tree for all events sharing a correlation ID