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Official MCP Ruby SDK

Official Ruby SDK for Model Context Protocol clients and servers, published as the `mcp` gem with JSON-RPC handling, tool, prompt, and resource registration, stdio and Streamable HTTP transports, Rack/Rails integration, roots, sampling, elicitation, logging, cancellation, pagination, and RubyGems metadata.

by Model Context Protocol·added 2026-06-18·

CLI

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Review first — review before installing

Open the source and read safety notes before installing.

Safety notes

The official Ruby SDK is a protocol library; risk comes from your registered tools, resources, prompts, transports, session handling, and framework integration.
Validate tool arguments, enforce caller permissions, bound file and network access, and sanitize exceptions before returning MCP responses.
The upstream README warns that Streamable HTTP session and SSE state are in memory by default; multi-process Rack/Rails deployments need stateless mode or sticky sessions.
Rails controller integrations that create servers per request should review user context, tool selection, and request-specific authorization carefully.

Privacy notes

Ruby MCP clients and servers may expose tool arguments, tool results, resource contents, prompt templates, request context, session IDs, logs, progress events, exceptions, and filesystem roots.
Avoid leaking secrets, customer data, private files, internal identifiers, stack traces, privileged paths, or session contents through schemas, responses, errors, or logs.
Document which MCP client, Ruby process, Rack/Rails layer, session store, model provider, transport, and logging system can observe each request.

Prerequisites

Ruby project compatible with the gem's required Ruby version and runtime dependencies.
A decision between local stdio integration, Rack/Rails Streamable HTTP, or client-side MCP usage.
A session strategy for Streamable HTTP when using Rack-compatible frameworks.
Authorization, side-effect, and data-exposure requirements for production tools and resources.

Schema details

Install type: cli
Troubleshooting: No

Source repository stats

Scope: Source repo

Collection metadata

Estimated setup: 20 minutes
Difficulty: intermediate

Tool listing metadata

Website: https://modelcontextprotocol.io
Pricing: free
Disclosure: editorial
Application category: DeveloperApplication
Operating system: Cross-platform

Full copyable content

gem install mcp

About this resource

Overview

The official MCP Ruby SDK is the Model Context Protocol project's Ruby implementation for building MCP clients and servers. It is published as the mcp gem and provides JSON-RPC handling, server and client APIs, transport implementations, capability registration, and framework-friendly deployment patterns.

Ruby demand is narrower than Python or TypeScript, but the search intent is clear: developers looking for a Ruby MCP SDK usually need a direct gem, Rack/Rails deployment guidance, or a way to expose existing Ruby application capabilities without another language bridge.

Install

Add the gem to a Gemfile:

gem "mcp"

Or install it directly:

gem install mcp

MCP Fit

Choose the official Ruby SDK when a Ruby application, Rails service, Rack app, CLI, or internal tool needs to act as an MCP server or client. It is especially useful when existing business logic already lives in Ruby and should be exposed through carefully reviewed tools or resources.

The SDK supports local stdio usage and Streamable HTTP. HTTP deployments need normal web-app review for sessions, auth, request routing, and error handling.

Core Capabilities

Area	Ruby SDK Coverage
Package	`mcp` gem on RubyGems
Server APIs	JSON-RPC 2.0 handling, initialization, capability negotiation, tools, prompts, resources, templates, roots, sampling, elicitation, logging, cancellation, and pagination
Client APIs	Connect to MCP servers and use tools, resources, prompts, completions, and capability extensions
Transports	stdio and Streamable HTTP, including SSE behavior
Frameworks	Rack-compatible transport with Rails mount and controller examples
Configuration	Exception reporter, around-request hooks, explicit configuration, and server context

Use Cases

Expose Rails or Ruby service methods as MCP tools.
Build a local Ruby MCP server over stdio.
Mount a Streamable HTTP MCP endpoint in Rails routes.
Create per-request Rails controller MCP servers with user context.
Build a Ruby MCP client for internal automation.
Add roots, sampling, elicitation, or capability extensions to Ruby workflows.

Source Review

Verified on 2026-06-18:

The upstream README identifies this as the official Ruby SDK for Model Context Protocol servers and clients.
The README documents Gemfile and gem install mcp installation paths.
The README covers JSON-RPC handling, tools, prompts, resources, stdio transport, Streamable HTTP, Rack/Rails usage, roots, sampling, elicitation, logging, cancellation, pagination, and configuration hooks.
The README warns that Streamable HTTP session and SSE state are stored in memory by default and need single-process, sticky-session, or stateless deployment choices.
mcp.gemspec declares gem name mcp, Apache-2.0 licensing, required Ruby version >= 2.7.0, documentation/source URLs, and json_schemer dependency.
RubyGems resolves package metadata for mcp.

Safety and Privacy

Ruby MCP servers can sit very close to Rails models, user data, background jobs, and internal services. Keep tool schemas narrow, validate arguments, check user authorization, and avoid returning raw exceptions or Active Record objects to clients.

For Streamable HTTP, treat session handling as a production design decision. Single-process state, sticky sessions, stateless mode, and per-request server construction all create different privacy and correctness boundaries.

Duplicate Check

Checked current content/mcp/, content/tools/, content/skills/, open pull requests, and repository-wide content for modelcontextprotocol/ruby-sdk, official MCP Ruby SDK, Model Context Protocol Ruby SDK, Ruby MCP server SDK, Ruby MCP client SDK, mcp Ruby gem, Rails MCP server, Rack MCP Streamable HTTP, and RubyGems MCP. No dedicated official Ruby SDK entry, exact source URL duplicate, target file, or open duplicate PR was found.

#ruby #mcp #sdk #gem #rails #official

Source citations

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How it compares

Official MCP Ruby SDK side by side with 3 alternatives on trust, install, platform support, and disclosed safety notes — all from reviewed registry metadata.

Field	Official MCP Ruby SDK Official Ruby SDK for Model Context Protocol clients and servers, published as the `mcp` gem with JSON-RPC handling, tool, prompt, and resource registration, stdio and Streamable HTTP transports, Rack/Rails integration, roots, sampling, elicitation, logging, cancellation, pagination, and RubyGems metadata. Open dossier	Official MCP Java SDK Official Java SDK for Model Context Protocol clients and servers, maintained in collaboration with Spring AI, with Java 17+ support, Maven artifacts, synchronous and asynchronous APIs, Reactive Streams, Project Reactor, JDK HttpClient, Servlet transport, JSON binding modules, and conformance tests. Open dossier	Official MCP Python SDK Official Python SDK for Model Context Protocol clients and servers, published as the `mcp` package on PyPI, with FastMCP server helpers, client support, tools, resources, prompts, stdio, SSE, Streamable HTTP, authentication, elicitation, sampling, logging, and standalone development tools. Open dossier	Official MCP Rust SDK Official Rust SDK for Model Context Protocol clients and servers, published as the `rmcp` crate with tokio async runtime support, server and client features, tool macros, resources, prompts, sampling, roots, logging, completions, notifications, Streamable HTTP, child-process transports, and OAuth support. Open dossier
Trust
Install risk	Review first	Review first	Review first	Review first
Notes	Safety ✓ Privacy ✓	Safety ✓ Privacy ✓	Safety ✓ Privacy ✓	Safety ✓ Privacy ✓
Category	tools	tools	tools	tools
Source	source-backed	source-backed	source-backed	source-backed
Author	Model Context Protocol	Model Context Protocol	Model Context Protocol	Model Context Protocol
Added	2026-06-18	2026-06-18	2026-06-18	2026-06-18
Platforms	CLI	CLI	CLI	CLI
Source repo	—	—	—	—
Safety notes	✓The official Ruby SDK is a protocol library; risk comes from your registered tools, resources, prompts, transports, session handling, and framework integration. Validate tool arguments, enforce caller permissions, bound file and network access, and sanitize exceptions before returning MCP responses. The upstream README warns that Streamable HTTP session and SSE state are in memory by default; multi-process Rack/Rails deployments need stateless mode or sticky sessions. Rails controller integrations that create servers per request should review user context, tool selection, and request-specific authorization carefully.	✓The official Java SDK is a protocol library; production risk comes from your MCP tools, resources, prompts, transports, authorization hooks, and framework integration. Validate tool inputs, enforce caller permissions, bound side effects, and avoid returning raw Java exceptions or internal stack details to MCP clients. Servlet, Spring, and remote transport deployments need authentication, TLS, request limits, observability policy, cancellation behavior, and abuse protection. Spring AI MCP security and annotation support may simplify integration, but application owners still need to review authorization, tenant boundaries, and data retention.	✓The official Python SDK is a protocol library; risk comes from the tools, resources, prompts, transports, auth flows, and server process you build with it. Validate all tool inputs, enforce caller permissions, bound file and network access, and sanitize errors before returning them to an MCP client. HTTP, SSE, and ASGI deployments need authentication, TLS, CORS review, host/path routing controls, request limits, logging policy, and abuse protection. The upstream README says v2 is alpha; production projects should stay on the stable v1 line unless they intentionally pin and test a pre-release.	✓The official Rust SDK is a protocol library; risk comes from the tools, resources, prompts, transports, auth flows, and long-running task behavior you implement with it. Validate tool parameters, enforce caller permissions, bound file and network access, and sanitize errors before returning MCP responses. Streamable HTTP servers, child-process transports, and OAuth flows need normal production controls: auth, TLS, request limits, lifecycle handling, logging policy, and abuse protection. Feature flags can pull in transport, HTTP, OAuth, schema, and process dependencies; review the enabled feature set before shipping.
Privacy notes	✓Ruby MCP clients and servers may expose tool arguments, tool results, resource contents, prompt templates, request context, session IDs, logs, progress events, exceptions, and filesystem roots. Avoid leaking secrets, customer data, private files, internal identifiers, stack traces, privileged paths, or session contents through schemas, responses, errors, or logs. Document which MCP client, Ruby process, Rack/Rails layer, session store, model provider, transport, and logging system can observe each request.	✓Java MCP clients and servers may expose tool arguments, tool results, resource contents, prompt templates, request metadata, correlation IDs, logs, traces, and authorization context. Avoid leaking secrets, customer data, private resources, internal identifiers, stack traces, privileged paths, or token values through schemas, responses, errors, or logs. Document which MCP client, server process, Java framework, model provider, transport, and observability system can observe each request.	✓MCP Python servers may expose local files, application data, tool arguments, tool results, resource contents, prompt templates, authentication state, logs, traces, and errors. Do not leak secrets, customer data, private paths, internal identifiers, token values, or privileged resource contents through schemas, examples, responses, or logs. Document which MCP client, model provider, server process, transport, ASGI layer, and observability system can observe each request.	✓Rust MCP services may expose tool arguments, tool results, resource contents, prompt templates, task state, authentication metadata, logs, traces, and subprocess output. Avoid returning secrets, private files, customer data, internal identifiers, privileged paths, or raw dependency/runtime errors to MCP clients. Document which MCP client, server process, transport, subprocess, model provider, and observability system can observe each request.
Prerequisites	Ruby project compatible with the gem's required Ruby version and runtime dependencies. A decision between local stdio integration, Rack/Rails Streamable HTTP, or client-side MCP usage. A session strategy for Streamable HTTP when using Rack-compatible frameworks. Authorization, side-effect, and data-exposure requirements for production tools and resources.	Java 17 or newer and a Maven or Gradle build configured for the selected SDK artifact version. A choice of core Java SDK usage, Spring AI MCP integration, or both. A target transport, such as stdio, JDK HttpClient, Servlet, WebFlux, WebMVC, or another framework path. Authentication, authorization, and data-exposure requirements for production clients and servers.	Python 3.10 or newer and a project managed with uv, pip, or another Python package manager. A decision between stable v1 usage and explicit v2 alpha testing with a pinned pre-release. A target transport, such as stdio for local tools or Streamable HTTP for hosted MCP servers. Clear authorization, side-effect, and data-exposure boundaries for production tools and resources.	Rust toolchain and Cargo project compatible with the SDK crate version and edition requirements. Tokio async-runtime familiarity for client, server, transport, and handler integration. A selected feature set for server, client, macros, Streamable HTTP, child-process, OAuth, or schema generation support. Reviewed authorization, side-effect, and data-exposure boundaries for production MCP tools and resources.
Install	`gem install mcp`	`mvn dependency:get -Dartifact=io.modelcontextprotocol.sdk:mcp:2.0.0`	`uv add "mcp[cli]"`	`cargo add rmcp`
Config	—	—	—	—
Citations	Source repositorygithub.com 2026-06-18T12:49:35+00:00 Documentationruby.sdk.modelcontextprotocol.io Websitemodelcontextprotocol.io	Source repositorygithub.com 2026-06-18T12:49:35+00:00 Documentationjava.sdk.modelcontextprotocol.io	Source repositorygithub.com 2026-06-18T12:49:35+00:00 Documentationpy.sdk.modelcontextprotocol.io	Source repositorygithub.com 2026-06-18T12:49:35+00:00 Documentationdocs.rs
Claim	Unclaimed	Unclaimed	Unclaimed	Unclaimed

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