Crate mcpkit_actix 

Actix-web integration for the Rust MCP SDK.

This crate provides integration between the MCP SDK and the Actix-web framework, making it easy to expose MCP servers over HTTP.

Features

• HTTP POST endpoint for JSON-RPC messages
• Server-Sent Events (SSE) streaming for notifications
• Session management with automatic cleanup
• Protocol version validation
• CORS support

HTTP Protocol Requirements

Clients must include the Mcp-Protocol-Version header in all requests:

POST /mcp HTTP/1.1
Content-Type: application/json
Mcp-Protocol-Version: 2025-11-25

{"jsonrpc":"2.0","id":1,"method":"initialize","params":{...}}

Supported protocol versions: 2024-11-05, 2025-03-26, 2025-06-18, 2025-11-25

Quick Start

use mcpkit::prelude::*;
use mcpkit_actix::{McpState, handle_mcp_post, handle_sse};
use actix_web::{web, App, HttpServer};

// Your MCP server handler (use #[mcp_server] macro)
#[mcp_server(name = "my-server", version = "1.0.0")]
impl MyServer {
    #[tool(description = "Say hello")]
    async fn hello(&self, name: String) -> ToolOutput {
        ToolOutput::text(format!("Hello, {name}!"))
    }
}

#[actix_web::main]
async fn main() -> std::io::Result<()> {
    // Create MCP state - no Clone required on handler!
    let state = McpState::new(MyServer::new());

    HttpServer::new(move || {
        App::new()
            .app_data(web::Data::new(state.clone()))
            .route("/mcp", web::post().to(handle_mcp_post::<MyServer>))
            .route("/mcp/sse", web::get().to(handle_sse::<MyServer>))
    })
    .bind("0.0.0.0:3000")?
    .run()
    .await
}

Client Example (curl)

# Initialize the connection
curl -X POST http://localhost:3000/mcp \
  -H "Content-Type: application/json" \
  -H "Mcp-Protocol-Version: 2025-11-25" \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-11-25","clientInfo":{"name":"test","version":"1.0"},"capabilities":{}}}'

# List available tools
curl -X POST http://localhost:3000/mcp \
  -H "Content-Type: application/json" \
  -H "Mcp-Protocol-Version: 2025-11-25" \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/list"}'

# Call a tool
curl -X POST http://localhost:3000/mcp \
  -H "Content-Type: application/json" \
  -H "Mcp-Protocol-Version: 2025-11-25" \
  -d '{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"hello","arguments":{"name":"World"}}}'

Modules

prelude

Prelude module for convenient imports.

Structs

EventStore

Event store for SSE message resumability.

EventStoreConfig

Configuration for event store retention.

McpRouter

Builder for MCP Actix routers.

McpState

Shared state for MCP Actix handlers.

OAuthState

State for OAuth discovery endpoints.

Session

A single MCP session.

SessionManager

Session manager for SSE connections.

SessionStore

Thread-safe session store with automatic cleanup.

StoredEvent

A stored SSE event for replay support.

Enums

ExtensionError

Errors that can occur in the Actix MCP extension.

Constants

SUPPORTED_VERSIONS

Protocol versions supported by this extension.

Functions

handle_mcp_post

Handle MCP POST requests.

handle_oauth_protected_resource

Handle .well-known/oauth-protected-resource requests.

handle_sse

Handle SSE connections for server-to-client streaming.

is_supported_version

Check if a protocol version is supported.