erlmcp

Erlang implementation of the Model Context Protocol (MCP) SDK.

MCP enables seamless communication between AI assistants and local services through a standardized protocol. This SDK provides both client and server implementations with full OTP compliance, allowing you to build robust, fault-tolerant integrations that expose resources, tools, and prompts to AI systems.

Installation

Requirements: Erlang/OTP 25 or later

%% rebar.config
{deps, [
    {erlmcp, "0.5.1"}
]}.

rebar3 compile

Quick Start

Creating an MCP Server

%% Start a server that exposes resources
{ok, Server} = erlmcp_server:start_link({stdio, []}, Capabilities),

%% Add a resource
erlmcp_server:add_resource(Server, >,
    fun(_Uri) -> > end),

%% Add a tool with JSON Schema validation
Schema = #{> => >,
           > => #{> => #{> => >}}},
erlmcp_server:add_tool_with_schema(Server, >,
    fun(#{> := Name}) ->
        >
    end, Schema).

Creating an MCP Client

%% Connect to an MCP server
{ok, Client} = erlmcp_client:start_link({stdio, []}, #{strict_mode => false}),

%% Initialize connection
{ok, _} = erlmcp_client:initialize(Client, Capabilities),

%% List available resources
{ok, #{> := Resources}} = erlmcp_client:list_resources(Client),

%% Call a tool
{ok, Result} = erlmcp_client:call_tool(Client, >,
                                        #{> => >}).

Examples

See the examples directory for comprehensive examples:

• Weather Server - Full MCP server with resources, tools, and subscriptions
• Calculator Client - Sophisticated client with connection management
• Complete Application - OTP application with supervision

Documentation

• Architecture Overview - System design and components
• Protocol Guide - MCP protocol implementation details
• OTP Patterns - Erlang/OTP best practices used
• API Reference - Complete API documentation

Key Features

• ✅ Full MCP protocol support (resources, tools, prompts)
• ✅ OTP-compliant with supervision trees
• ✅ Multiple transport layers (stdio, TCP, HTTP)
• ✅ JSON Schema validation for tools
• ✅ Resource subscriptions with notifications
• ✅ Automatic reconnection with backoff
• ✅ Comprehensive error handling
• ✅ Production-ready logging and monitoring

License

Apache 2.0

External Resources

• Get started with the Model Context Protocol (MCP)