MCP over SSE

@kEND

Basic information

About MCP over SSE

An elixir Model Context Protocal (MCP) server library which uses the Server-Sent Events (SSE) transport type

MCP over SSE config

Add this server to your MCP-compatible client using the configuration below.

{
  "mcpServers": {
    "mcp_sse": {
      "command": "npx",
      "args": [
        "@modelcontextprotocol/inspector@latest"
      ],
      "env": {
        "MCP_SERVER_URL": "localhost:4000"
      }
    }
  }
}

MCP over SSE tools

Tool list not available yet

This listing does not currently have a tool list to display. This does not mean the server has no tools; check its documentation for supported capabilities.

Fetch the live tool list by running this server in a temporary sandbox using the button above.

Overview

What is MCP over SSE?

MCP over SSE is an Elixir library that provides a simple implementation of the Model Context Protocol (MCP) using Server-Sent Events. It is intended for developers building MCP servers with Phoenix or Plug/Bandit applications.

How to use MCP over SSE?

Add the library as a dependency, configure MIME types and the MCP server module, implement the MCPServer behaviour, and set up routing for the /sse and /message endpoints. Run your application with mix phx.server or mix run --no-halt. Connect clients such as MCP Inspector or Cursor to the SSE endpoint.

Key features of MCP over SSE

Full MCP server implementation over SSE
JSON-RPC message handling
Tool registration and execution
Automatic ping/keepalive
Session management with auto-generated IDs
Error handling and validation

Use cases of MCP over SSE

Build custom MCP servers in Elixir for AI tool integration
Connect AI assistants like Cursor using SSE
Test MCP tools interactively with MCP Inspector
Handle multiple client sessions with automatic session ID generation

Frequently asked questions

What are the dependencies and runtime requirements?

Requires Elixir and either a Phoenix application or a Plug application with Bandit. The library depends on `:mime`, `:mcp_sse`, and optionally `:plug` and `:bandit`.

How does session management work?

Each connection must have a session ID. If the client does not provide one, the server automatically generates a new session ID and attaches it to query parameters for both the SSE and message endpoints.

What transport does MCP over SSE use?

It uses Server-Sent Events (SSE) for server-to-client messages and HTTP POST for client-to-server JSON-RPC requests, both over configurable paths.

Can I customize the endpoints and keepalive interval?

Yes. You can configure `sse_path`, `message_path`, and `sse_keepalive_timeout` (in milliseconds) in your application config. Setting the timeout to `:infinity` disables keepalive pings.

How should MCP tool responses be formatted?

Responses must follow the MCP specification. Supported content types are `text`, `image`, and `resource`. For structured data, convert it to a formatted JSON string using a JSON encoder.

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