quickstart-resources/mcp-client-ruby

An LLM-Powered Chatbot MCP Client written in Ruby

An interactive chatbot MCP client: it launches an MCP server over stdio, lists its tools, and hands them to Claude, which can call them while answering your questions.

This example accompanies the Build an MCP client tutorial.

Prerequisites

• Ruby 3.4+ (3.3 also satisfies the gems)
• Bundler
• An Anthropic API key (optional — see below)

Setup

Install the gems, then put your API key in a .env file (or export ANTHROPIC_API_KEY in your shell):

bundle install
cp .env.example .env
# then edit .env and add your key

Run the client

Pass the path to a server script. .rb servers are launched with ruby, .py with python3, and .js with node:

bundle exec ruby client.rb ../weather-server-ruby/weather.rb

Type a question (for example, "What's the weather in Sacramento?") and Claude answers using the server's tools. Type quit to exit.

Without an ANTHROPIC_API_KEY, the client still connects, prints the server's tools, and exits — useful for verifying the MCP wiring without credentials.

Structured content

The spec says clients SHOULD validate structured results against the schema the tool declares, and this SDK's client does not do it for you — MCP::Client::Tool#output_schema hands back the raw schema from the wire and nothing checks results against it. So the client compiles each declared schema once at connect time with MCP::Tool::OutputSchema.new and validates every non-error result.

The two channels go to different readers: content is forwarded to the model, while structured_content is used as data — when a tool returns an array, the client counts its items rather than re-reading the prose. See Structured Content.

MCP::Client::Stdio offers 2026-07-28 by default, so no negotiation setup is needed here.