🔍 Rust MCP Server + Inspector Example: SSE Transport with an Add Tool

credit : https://dev.to/joshmo_dev/using-model-context-protocol-with-rig-m7o

This project demonstrates how to set up an MCP (Model Context Protocol) server and client using Server-Sent Events (SSE) for communication. It includes a simple tool that adds two numbers and integrates with the RIG agent for LLM prompting.

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🚀 Getting Started

Clone this repo and run with:

cargo run

In a separate terminal start the MCP Inspector with:

npx @modelcontextprotocol/inspector sse http://127.0.0.1:3001/sse

You'll see output like:

Starting MCP inspector...
Proxy server listening on port 3000
New SSE connection
Query parameters: { transportType: 'sse', url: 'http://localhost:3001/sse' }
SSE transport: url=http://localhost:3001/sse, headers=
Connected to SSE transport
Connected MCP client to backing server transport
Created web app transport
Set up MCP proxy
🔍 MCP Inspector is up and running at http://localhost:5173 🚀

You can now view the web interface at http://localhost:5173

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🛠️ Features

• ✅ Sets up a custom MCP server using ServerSseTransport
• ✅ Connects a MCP client to the server
• ✅ Registers a custom tool: AddTool, which adds two numbers
• ✅ Lists registered tools via MCP
• ✅ Integrates with RIG and prompts an LLM agent using the tool

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🧠 Code Overview

#[tool(
    name = "Add",
    description = "Adds two numbers together.",
    params(a = "The first number to add", b = "The second number to add")
)]
async fn add_tool(a: f64, b: f64) -> Result {
    Ok(tool_text_content!((a + b).to_string()))
}

This defines the Add tool that is registered in the MCP server.

The main function sets up:

• Tracing
• The MCP server and transport (SSE)
• A MCP client that initializes and lists available tools
• A RIG agent with OpenAI backend, which uses the MCP tool

The agent then runs a prompt:

let response = agent.prompt("Add 10 + 10").await;

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🧪 Sample Output

When run successfully, you'll see logs like:

Initialized: Ok(...)
Tools: Ok([...])
Building RIG agent
Prompting RIG agent
Agent response: Some("20")

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🧰 Tech Stack

• 🦀 Rust with tokio
• 📡 SSE transport from mcp_core
• 🔧 MCP server/client architecture
• 🤖 RIG agent with OpenAI model
• 🌐 MCP Inspector web interface

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📦 Dependencies

Make sure you have these in your Cargo.toml:

[dependencies]
tokio = { version = "1", features = ["full"] }
anyhow = "1"
serde_json = "1"
mcp_core = "..."
mcp_core_macros = "..."
rig = "..."

Replace ... with the appropriate versions based on your environment.

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📍 Inspector GUI

Visit http://localhost:5173 to view and interact with the MCP Inspector UI.

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✅ Test Log Sample

Query parameters: { transportType: 'sse', url: 'http://localhost:3001/sse' }
Connected to SSE transport
Connected MCP client to backing server transport
Set up MCP proxy
Received message for sessionId cdd4a8be-57e2-44e3-9b81-3df300e86f22

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📬 Questions or Feedback?

Feel free to open an issue or start a discussion!

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